ostd/mm/page_table/

mod.rs

// SPDX-License-Identifier: MPL-2.0
use vstd::arithmetic::power2::*;
use vstd::prelude::*;
use vstd::simple_pptr;
use vstd::std_specs::clone::*;
use vstd_extra::assert;
use vstd_extra::panic::may_panic;
use vstd_extra::prelude::*;

use crate::specs::arch::*;
use crate::specs::mm::page_table::{cursor::*, *};
use crate::specs::task::InAtomicMode;

use crate::mm::frame::meta::{REF_COUNT_MAX, REF_COUNT_UNIQUE, REF_COUNT_UNUSED};
use crate::mm::kspace::kvirt_area::disable_preempt;
use crate::specs::mm::{
    frame::{mapping::frame_to_index, meta_region_owners::MetaRegionOwners},
    page_table::{
        is_valid_range_spec, nr_pte_index_bits_spec, pte_index_bit_offset_spec,
        top_level_index_width_spec, vaddr_range_spec,
    },
};

use core::{
    fmt::Debug,
    intrinsics::transmute_unchecked,
    ops::{Range, RangeInclusive},
    sync::atomic::Ordering,
};

use super::{
    Paddr, PagingConstsTrait, PagingLevel, PodOnce, Vaddr,
    kspace::KernelPtConfig,
    nr_subpage_per_huge,
    page_prop::{CachePolicy, PageProperty},
    page_size,
    vm_space::UserPtConfig,
};

use crate::{
    //task::{atomic_mode::AsAtomicModeGuard, disable_preempt},
    Pod,
    arch::mm::{PageTableEntry, PagingConsts},
};

mod node;
pub use node::*;
mod cursor;

pub(crate) use cursor::*;

#[cfg(ktest)]
mod test;

//pub(crate) mod boot_pt;

verus! {

#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub enum PageTableError {
    /// The provided virtual address range is invalid.
    InvalidVaddrRange(Vaddr, Vaddr),
    /// The provided virtual address is invalid.
    InvalidVaddr(Vaddr),
    /// Using virtual address not aligned.
    UnalignedVaddr,
}

pub trait RCClone: Sized {
    spec fn clone_requires(self, perm: MetaRegionOwners) -> bool;

    spec fn clone_ensures(
        self,
        old_perm: MetaRegionOwners,
        new_perm: MetaRegionOwners,
        res: Self,
    ) -> bool;

    fn clone(&self, Tracked(perm): Tracked<&mut MetaRegionOwners>) -> (res: Self)
        requires
            self.clone_requires(*old(perm)),
        ensures
    // RCClone::clone` doesn't mint/redeem segment obligations.
    // The per-frame `frame_obligations` effect is left to each impl's `clone_ensures`

            res == *self,
            self.clone_ensures(*old(perm), *final(perm), res),
            final(perm).inv(),
            final(perm).slots == old(perm).slots,
            final(perm).slot_owners.dom() == old(perm).slot_owners.dom(),
    ;
}

/// The configurations of a page table.
///
/// It abstracts away both the usage and the architecture specifics from the
/// general page table implementation. For examples:
///  - the managed virtual address range;
///  - the trackedness of physical mappings;
///  - the PTE layout;
///  - the number of page table levels, etc.
///
/// # Safety
///
/// The implementor must ensure that the `item_into_raw` and `item_from_raw`
/// are implemented correctly so that:
///  - `item_into_raw` consumes the ownership of the item;
///  - if the provided raw form matches the item that was consumed by
///    `item_into_raw`, `item_from_raw` restores the exact item that was
///    consumed by `item_into_raw`.
pub unsafe trait PageTableConfig: Clone + Debug + Send + Sync + 'static {
    spec fn TOP_LEVEL_INDEX_RANGE_spec() -> Range<usize>;

    /// The index range at the top level (`C::NR_LEVELS()`) page table.
    ///
    /// When configured with this value, the [`PageTable`] instance will only
    /// be allowed to manage the virtual address range that is covered by
    /// this range. The range can be smaller than the actual allowed range
    /// specified by the hardware MMU (limited by `C::ADDRESS_WIDTH`).
    #[verifier::when_used_as_spec(TOP_LEVEL_INDEX_RANGE_spec)]
    fn TOP_LEVEL_INDEX_RANGE() -> Range<usize>
        returns
            Self::TOP_LEVEL_INDEX_RANGE(),
    ;

    /// VERIFICATION only: The leading bits `[48, 64)` of every virtual address managed by this
    /// config.
    ///
    /// Concretely, a mapping `m` in this page table has
    /// `m.va_range.start / 2^48 == LEADING_BITS_spec()`. For non-sign-extended
    /// configurations (e.g. `UserPtConfig`) this is `0`. For x86-64 kernel
    /// PT it is `0xffff` (sign-extended high half). The type is wide enough
    /// to carry arbitrary bit patterns, so the model can accommodate future
    /// configurations that place their managed range at a non-canonical
    /// fixed offset.
    ///
    /// Combined with `TOP_LEVEL_INDEX_RANGE`, this fully determines
    /// the managed VA range, computed as
    /// [`vaddr_range_spec::<Self>`]. Callers that previously used
    /// `VADDR_RANGE_spec()` should use `vaddr_range_spec::<C>()`
    /// directly — the inclusive `(start, end_inclusive)` form avoids the
    /// `end == usize::MAX + 1` overflow that plagues `Range<Vaddr>` for
    /// sign-extended kernel configurations.
    open spec fn LEADING_BITS_spec() -> usize {
        0
    }

    open spec fn TOP_LEVEL_CAN_UNMAP_spec() -> bool {
        true
    }

    /// If we can remove the top-level page table entries.
    ///
    /// This is for the kernel page table, whose second-top-level page
    /// tables need `'static` lifetime to be shared with user page tables.
    /// Other page tables do not need to set this to `false`.
    #[verifier::when_used_as_spec(TOP_LEVEL_CAN_UNMAP_spec)]
    fn TOP_LEVEL_CAN_UNMAP() -> bool
        returns
            Self::TOP_LEVEL_CAN_UNMAP(),
    ;

    /// VERIFICATION only: Upper bound on `locked_range().end` for cursors of this config.
    ///
    /// May be tighter than the structural `vaddr_range_spec().1 + 1`
    /// when the actual sources of cursor ranges (e.g. the kvirt allocator
    /// for `KernelPtConfig`) draw from a sub-window of the configured VA
    /// range. `KernelPtConfig` overrides this to `FRAME_METADATA_BASE_VADDR`,
    /// which the `kvirt_alloc_range_bounds` axiom enforces. This bound is
    /// what allows the cursor's `move_forward` proof to discharge
    /// `prefix.idx[NR_LEVELS - 1] + 1 < NR_ENTRIES` at the top-level
    /// boundary — the structural bound only gives `<= NR_ENTRIES` for
    /// configurations whose `TOP_LEVEL_INDEX_RANGE.end == NR_ENTRIES`.
    ///
    /// Default: `usize::MAX + 1` (no tightening over the structural bound).
    open spec fn LOCKED_END_BOUND_spec() -> int {
        0x1_0000_0000_0000_0000int
    }

    /// The type of the page table entry.
    type E: PageTableEntryTrait;

    /// The paging constants.
    type C: PagingConstsTrait;

    /// The item that can be mapped into the virtual memory space using the
    /// page table.
    ///
    /// Usually, this item is a [`crate::mm::Frame`], which we call a "tracked"
    /// frame. The page table can also do "untracked" mappings that only maps
    /// to certain physical addresses without tracking the ownership of the
    /// mapped physical frame. The user of the page table APIs can choose by
    /// defining this type and the corresponding methods [`item_into_raw`] and
    /// [`item_from_raw`].
    ///
    /// [`item_from_raw`]: PageTableConfig::item_from_raw
    /// [`item_into_raw`]: PageTableConfig::item_into_raw
    type Item: RCClone;

    spec fn item_into_raw_spec(item: Self::Item) -> (Paddr, PagingLevel, PageProperty);

    /// Consumes the item and returns the physical address, the paging level,
    /// and the page property.
    ///
    /// The ownership of the item will be consumed, i.e., the item will be
    /// forgotten after this function is called.
    #[verifier::when_used_as_spec(item_into_raw_spec)]
    fn item_into_raw(item: Self::Item) -> ((paddr, level, prop): (Paddr, PagingLevel, PageProperty))
        requires
            Self::item_well_formed(item),
        ensures
            1 <= level <= NR_LEVELS,
            valid_frame_paddr(paddr),
            paddr % page_size(level) == 0,
            paddr + page_size(level) <= MAX_PADDR,
            Self::raw_item_well_formed(paddr, level, prop),
            Self::E::new_page_req(paddr, level, prop),
        returns
            Self::item_into_raw_spec(item),
    ;

    spec fn item_from_raw_spec(paddr: Paddr, level: PagingLevel, prop: PageProperty) -> Self::Item;

    /// Restores the item from the physical address and the paging level.
    ///
    /// There could be transformations after [`PageTableConfig::item_into_raw`]
    /// and before [`PageTableConfig::item_from_raw`], which include:
    ///  - splitting and coalescing the items, for example, splitting one item
    ///    into 512 `level - 1` items with and contiguous physical addresses;
    ///  - protecting the items, for example, changing the page property.
    ///
    /// Splitting and coalescing maintains ownership rules, i.e., if one
    /// physical address is within the range of one item, after splitting/
    /// coalescing, there should be exactly one item that contains the address.
    ///
    /// # Safety
    ///
    /// The caller must ensure that:
    ///  - the physical address and the paging level represent a page table
    ///    item or part of it (as described above);
    ///  - either the ownership of the item is properly transferred to the
    ///    return value, or the return value is wrapped in a
    ///    [`core::mem::ManuallyDrop`] that won't outlive the original item.
    ///
    /// A concrete trait implementation may require the caller to ensure that
    ///  - the [`super::PageFlags::AVAIL1`] flag is the same as that returned
    ///    from [`PageTableConfig::item_into_raw`].
    #[verifier::when_used_as_spec(item_from_raw_spec)]
    unsafe fn item_from_raw(paddr: Paddr, level: PagingLevel, prop: PageProperty) -> (res:
        Self::Item)
        requires
            valid_frame_paddr(paddr),
            Self::raw_item_well_formed(paddr, level, prop),
        ensures
            Self::item_well_formed(res),
        returns
            Self::item_from_raw_spec(paddr, level, prop),
    ;

    /// Whether cloning this item bumps a slot's refcount. For ref-counted items
    /// (e.g. `MappedItem::Tracked`), `true`; for items where clone is a no-op
    /// (e.g. `MappedItem::Untracked` for kernel MMIO frames), `false`.
    spec fn tracked(item: Self::Item) -> bool;

    /// Per-config predicate that captures the structural well-formedness an item
    /// reconstructed via [`PageTableConfig::item_from_raw`] must satisfy. This may include both
    /// ownership invariants and restrictions on raw-only property bits.
    spec fn item_well_formed(item: Self::Item) -> bool;

    /// Per-config predicate that captures the well-formedness of raw properties
    /// produced via [`PageTableConfig::item_into_raw`] must satisfy.
    spec fn raw_item_well_formed(pa: Paddr, level: PagingLevel, prop: PageProperty) -> bool;

    /// Changing properties without changing trackedness preserves a canonical raw item.
    proof fn lemma_raw_item_well_formed_preserved(
        pa: Paddr,
        level: PagingLevel,
        old_prop: PageProperty,
        new_prop: PageProperty,
    )
        requires
            valid_frame_paddr(pa),
            Self::raw_item_well_formed(pa, level, old_prop),
            Self::tracked(Self::item_from_raw(pa, level, new_prop)) == Self::tracked(
                Self::item_from_raw(pa, level, old_prop),
            ),
        ensures
            Self::raw_item_well_formed(pa, level, new_prop),
    ;

    /// Splitting a canonical huge-page raw item yields canonical child raw items.
    proof fn lemma_raw_item_well_formed_split(
        pa: Paddr,
        level: PagingLevel,
        prop: PageProperty,
        child_pa: Paddr,
        child_idx: usize,
    )
        requires
            valid_frame_paddr(pa),
            Self::raw_item_well_formed(pa, level, prop),
            Self::E::new_page_req(pa, level, prop),
            level > 1,
            child_idx < NR_ENTRIES,
            child_pa == pa + child_idx * page_size((level - 1) as PagingLevel),
        ensures
            Self::raw_item_well_formed(child_pa, (level - 1) as PagingLevel, prop),
            Self::E::new_page_req(child_pa, (level - 1) as PagingLevel, prop),
    ;

    /// The item produced by [`PageTableConfig::item_from_raw`] is well-formed.
    proof fn lemma_item_from_raw_well_formed(pa: Paddr, level: PagingLevel, prop: PageProperty)
        requires
            valid_frame_paddr(pa),
            Self::raw_item_well_formed(pa, level, prop),
        ensures
            Self::item_well_formed(Self::item_from_raw(pa, level, prop)),
    ;

    /// Re-encoding a canonical raw item preserves the complete raw representation.
    proof fn lemma_item_into_raw_roundtrip(pa: Paddr, level: PagingLevel, prop: PageProperty)
        requires
            valid_frame_paddr(pa),
            Self::raw_item_well_formed(pa, level, prop),
        ensures
            Self::item_into_raw(Self::item_from_raw(pa, level, prop)) == (pa, level, prop),
    ;

    /// Decoding the raw representation produced from a well-formed item restores that item.
    proof fn lemma_item_from_raw_roundtrip(
        item: Self::Item,
        pa: Paddr,
        level: PagingLevel,
        prop: PageProperty,
    )
        requires
            valid_frame_paddr(pa),
            Self::item_well_formed(item),
            Self::item_into_raw(item) == (pa, level, prop),
        ensures
            Self::item_from_raw(pa, level, prop) == item,
    ;

    /// Proves that `clone_ensures` for `Self::Item` implies concrete per-field
    /// properties on `MetaRegionOwners`. Each `PageTableConfig` implementor proves
    /// this by unfolding its `MappedItem::clone_ensures` → `Frame::clone_ensures`.
    /// Proves that after `clone`, the slot at `frame_to_index(pa)` has the expected
    /// per-field properties. Implementors unfold their `MappedItem::clone_ensures` to
    /// `Frame::clone_ensures` and connect `pa` to the frame's internal pointer address.
    proof fn lemma_clone_ensures_concrete(
        item: Self::Item,
        pa: Paddr,
        old_regions: MetaRegionOwners,
        new_regions: MetaRegionOwners,
        res: Self::Item,
    )
        requires
            item.clone_ensures(old_regions, new_regions, res),
            Self::item_into_raw_spec(item).0 == pa,
            res == item,
            new_regions.inv(),
            new_regions.slots =~= old_regions.slots,
            new_regions.slot_owners.dom() =~= old_regions.slot_owners.dom(),
        ensures
    // Other slots always unchanged.

            forall|i: int|
                i != frame_to_index(pa) ==> (#[trigger] new_regions.slot_owners[i]
                    == old_regions.slot_owners[i]),
            // The frame's slot: bumped if the item is ref-counted, otherwise unchanged.
            Self::tracked(item) ==> {
                &&& new_regions.slot_owner(pa).ref_count() == old_regions.slot_owner(pa).ref_count()
                    + 1
                &&& new_regions.slot_owner(pa).ref_count_perm.id() == old_regions.slot_owner(
                    pa,
                ).ref_count_perm.id()
                &&& new_regions.slot_owner(pa).storage_perm() == old_regions.slot_owner(
                    pa,
                ).storage_perm()
                &&& new_regions.slot_owner(pa).vtable_ptr_perm() == old_regions.slot_owner(
                    pa,
                ).vtable_ptr_perm()
                &&& new_regions.slot_owner(pa).in_list_perm == old_regions.slot_owner(
                    pa,
                ).in_list_perm
                &&& new_regions.slot_owner(pa).paths_in_pt == old_regions.slot_owner(pa).paths_in_pt
                &&& new_regions.slot_owner(pa).slot_vaddr == old_regions.slot_owner(pa).slot_vaddr
                &&& new_regions.slot_owner(pa).usage == old_regions.slot_owner(pa).usage
            },
            !Self::tracked(item) ==> new_regions.slot_owner(pa) == old_regions.slot_owner(pa),
            // Canonical model: a tracked clone MINTS one per-frame obligation
            // at the slot (`Frame::clone`); an untracked clone is net-zero.
            Self::tracked(item) ==> new_regions.frame_obligations
                == old_regions.frame_obligations.insert(frame_to_index(pa)),
            !Self::tracked(item) ==> new_regions.frame_obligations == old_regions.frame_obligations,
    ;

    /// Proves `item.clone_requires(regions)` from the concrete frame-slot facts
    /// delivered by `metaregion_sound` plus the non-saturation bound propagated
    /// from `Cursor::query`. Implementors unfold their `MappedItem::clone_requires`
    /// to `Frame::clone_requires` and connect `pa` to the frame's internal pointer
    /// address.
    proof fn lemma_clone_requires_concrete(
        item: Self::Item,
        pa: Paddr,
        level: PagingLevel,
        prop: PageProperty,
        regions: MetaRegionOwners,
    )
        requires
            regions.inv(),
            Self::item_from_raw_spec(pa, level, prop) == item,
            Self::raw_item_well_formed(pa, level, prop),
            valid_frame_paddr(pa),
            regions.contains(frame_to_index(pa)),
            Self::tracked(item) ==> regions.slot_owner(pa).ref_count() > 0,
            // `rc != UNUSED` is needed only for tracked frames (untracked clone is a no-op).
            Self::tracked(item) ==> regions.slot_owner(pa).ref_count() != REF_COUNT_UNUSED,
            // Saturation aborts (Arc-style) via `inc_ref_count`'s diverging panic.
            Self::tracked(item) ==> (regions.slot_owner(pa).ref_count() < REF_COUNT_MAX
                || may_panic()),
        ensures
            item.clone_requires(regions),
    ;

    /// The requirements of the page table configuration constants so that the memory management system can work correctly.
    ///
    /// NOTE: The postcondition is designed to be minimal, to actually be used in proofs, call `lemma_page_table_config_constant_properties`
    /// instead to get all the properties that are derived from the requirements.
    ///
    /// FIXME： General architecture support. Move properties only relevant to paging constants to `PagingConstsTrait`.
    proof fn lemma_page_table_config_constant_requirements()
        ensures
            core::mem::size_of::<Self::E>() == Self::C::PTE_SIZE(),
            Self::TOP_LEVEL_INDEX_RANGE().start < Self::TOP_LEVEL_INDEX_RANGE().end,
            Self::TOP_LEVEL_INDEX_RANGE().end <= pow2(
                (Self::C::ADDRESS_WIDTH() - pte_index_bit_offset_spec::<Self::C>(
                    Self::C::NR_LEVELS(),
                )) as nat,
            ),
            Self::TOP_LEVEL_INDEX_RANGE().end * pow2(
                pte_index_bit_offset_spec::<Self::C>(Self::C::NR_LEVELS()) as nat,
            ) <= usize::MAX,
            Self::LEADING_BITS_spec() != 0usize ==> (Self::C::VA_SIGN_EXT() && ((
            Self::TOP_LEVEL_INDEX_RANGE().start * pow2(
                pte_index_bit_offset_spec::<Self::C>(Self::C::NR_LEVELS()) as nat,
            )) / (pow2((Self::C::ADDRESS_WIDTH() - 1) as nat) as int)) % 2 == 1),
            (Self::C::VA_SIGN_EXT() && (((Self::TOP_LEVEL_INDEX_RANGE().start * pow2(
                pte_index_bit_offset_spec::<Self::C>(Self::C::NR_LEVELS()) as nat,
            )) / (pow2((Self::C::ADDRESS_WIDTH() - 1) as nat) as int)) % 2 == 1)) ==> {
                &&& Self::LEADING_BITS_spec() * 0x1_0000_0000_0000int == 0x1_0000_0000_0000_0000int
                    - pow2(Self::C::ADDRESS_WIDTH() as nat)
            },
            Self::LEADING_BITS_spec() < 0x1_0000_usize,
            // FIXME: This property does not hold in general, `ADDRESS_WIDTH` can be wider.
            pow2(
                (Self::C::ADDRESS_WIDTH() - pte_index_bit_offset_spec::<Self::C>(
                    Self::C::NR_LEVELS(),
                )) as nat,
            ) == NR_ENTRIES,
    ;

    // The derived properties of the page table config constants.
    ///
    /// NOTE: Implementations of `PageTableConfig` do not need to implement this lemma, the proof is automatically inherited from the default implementation.
    proof fn lemma_page_table_config_constant_properties()
        ensures
    // Derived properties.

            Self::TOP_LEVEL_INDEX_RANGE().end <= NR_ENTRIES,
            // Copied from the postcondition of `lemma_page_table_config_constant_requirements`
            // so that we only need to call this lemma in proofs.
            core::mem::size_of::<Self::E>() == Self::C::PTE_SIZE(),
            Self::TOP_LEVEL_INDEX_RANGE().start < Self::TOP_LEVEL_INDEX_RANGE().end,
            Self::TOP_LEVEL_INDEX_RANGE().end <= pow2(
                (Self::C::ADDRESS_WIDTH() - pte_index_bit_offset_spec::<Self::C>(
                    Self::C::NR_LEVELS(),
                )) as nat,
            ),
            Self::TOP_LEVEL_INDEX_RANGE().end * pow2(
                pte_index_bit_offset_spec::<Self::C>(Self::C::NR_LEVELS()) as nat,
            ) <= usize::MAX,
            Self::LEADING_BITS_spec() != 0usize ==> (Self::C::VA_SIGN_EXT() && ((
            Self::TOP_LEVEL_INDEX_RANGE().start * pow2(
                pte_index_bit_offset_spec::<Self::C>(Self::C::NR_LEVELS()) as nat,
            )) / (pow2((Self::C::ADDRESS_WIDTH() - 1) as nat) as int)) % 2 == 1),
            (Self::C::VA_SIGN_EXT() && (((Self::TOP_LEVEL_INDEX_RANGE().start * pow2(
                pte_index_bit_offset_spec::<Self::C>(Self::C::NR_LEVELS()) as nat,
            )) / (pow2((Self::C::ADDRESS_WIDTH() - 1) as nat) as int)) % 2 == 1)) ==> {
                &&& Self::LEADING_BITS_spec() * 0x1_0000_0000_0000int == 0x1_0000_0000_0000_0000int
                    - pow2(Self::C::ADDRESS_WIDTH() as nat)
            },
            Self::LEADING_BITS_spec() < 0x1_0000_usize,
            // FIXME: This property does not hold in general, `ADDRESS_WIDTH` can be wider.
            pow2(
                (Self::C::ADDRESS_WIDTH() - pte_index_bit_offset_spec::<Self::C>(
                    Self::C::NR_LEVELS(),
                )) as nat,
            ) == NR_ENTRIES,
    {
        Self::C::lemma_paging_consts_properties();
        Self::lemma_page_table_config_constant_requirements();
    }
}

// Implement it so that we can comfortably use low level functions
// like `page_size::<C>` without typing `C::C` everywhere.
impl<C: PageTableConfig> PagingConstsTrait for C {
    open spec fn BASE_PAGE_SIZE_spec() -> usize {
        C::C::BASE_PAGE_SIZE_spec()
    }

    fn BASE_PAGE_SIZE() -> usize {
        C::C::BASE_PAGE_SIZE()
    }

    open spec fn NR_LEVELS_spec() -> PagingLevel {
        C::C::NR_LEVELS_spec()
    }

    fn NR_LEVELS() -> PagingLevel {
        proof {
            assert(Self::NR_LEVELS() == C::C::NR_LEVELS());
        }
        C::C::NR_LEVELS()
    }

    open spec fn HIGHEST_TRANSLATION_LEVEL_spec() -> PagingLevel {
        C::C::HIGHEST_TRANSLATION_LEVEL_spec()
    }

    fn HIGHEST_TRANSLATION_LEVEL() -> PagingLevel {
        C::C::HIGHEST_TRANSLATION_LEVEL()
    }

    open spec fn PTE_SIZE_spec() -> usize {
        C::C::PTE_SIZE_spec()
    }

    fn PTE_SIZE() -> usize {
        C::C::PTE_SIZE()
    }

    open spec fn ADDRESS_WIDTH_spec() -> usize {
        C::C::ADDRESS_WIDTH_spec()
    }

    fn ADDRESS_WIDTH() -> usize {
        C::C::ADDRESS_WIDTH()
    }

    open spec fn VA_SIGN_EXT_spec() -> bool {
        C::C::VA_SIGN_EXT_spec()
    }

    fn VA_SIGN_EXT() -> bool {
        C::C::VA_SIGN_EXT()
    }

    proof fn lemma_paging_consts_requirements() {
        C::C::lemma_paging_consts_requirements();
    }
}

/// Splits the address range into largest page table items.
///
/// Each of the returned items is a tuple of the physical address and the
/// paging level. It is helpful when you want to map a physical address range
/// into the provided virtual address.
///
/// For example, on x86-64, `C: PageTableConfig` may specify level 1 page as
/// 4KiB, level 2 page as 2MiB, and level 3 page as 1GiB. Suppose that the
/// supplied physical address range is from `0x3fdff000` to `0x80002000`,
/// and the virtual address is also `0x3fdff000`, the following 5 items will
/// be returned:
///
/// ```text
/// 0x3fdff000                                                 0x80002000
/// start                                                             end
///   |----|----------------|--------------------------------|----|----|
///    4KiB      2MiB                       1GiB              4KiB 4KiB
/// ```
///
/// # Panics
///
/// Panics if:
///  - any of `va`, `pa`, or `len` is not aligned to the base page size;
///  - the range `va..(va + len)` is not valid for the page table.
#[verifier::external_body]
pub fn largest_pages<C: PageTableConfig>(
    mut va: Vaddr,
    mut pa: Paddr,
    mut len: usize,
) -> impl Iterator<Item = (Paddr, PagingLevel)> {
    assert_eq!(va % C::BASE_PAGE_SIZE(), 0);
    assert_eq!(pa % C::BASE_PAGE_SIZE(), 0);
    assert_eq!(len % C::BASE_PAGE_SIZE(), 0);
    assert!(is_valid_range::<C>(&(va..(va + len))));

    core::iter::from_fn(
        move ||
            {
                if len == 0 {
                    return None;
                }
                let mut level = C::HIGHEST_TRANSLATION_LEVEL();
                while page_size(level) > len || va % page_size(level) != 0 || pa % page_size(level)
                    != 0 {
                    level -= 1;
                }

                let item_start = pa;
                va += page_size(level);
                pa += page_size(level);
                len -= page_size(level);

                Some((item_start, level))
            },
    )
}

/// Gets the top-level index width, in bits, for the page table.
fn top_level_index_width<C: PageTableConfig>() -> (ret: usize)
    returns
        top_level_index_width_spec::<C>(),
{
    proof {
        C::lemma_paging_consts_properties();
        C::lemma_page_table_config_constant_properties();
    }

    C::ADDRESS_WIDTH() - pte_index_bit_offset::<C>(C::NR_LEVELS())
}

fn pt_va_range_start<C: PageTableConfig>() -> (ret: Vaddr)
    ensures
        ret == C::TOP_LEVEL_INDEX_RANGE().start * pow2(
            pte_index_bit_offset_spec::<C>(C::NR_LEVELS()) as nat,
        ),
{
    proof {
        C::lemma_paging_consts_properties();
        let ghost idx_start = C::TOP_LEVEL_INDEX_RANGE().start;
        let ghost offset = pte_index_bit_offset_spec::<C>(C::NR_LEVELS());
        crate::specs::mm::page_table::vaddr_range_proofs::lemma_pt_va_range_start_shift_facts::<C>(
            idx_start,
            offset,
        );
        vstd::bits::lemma_usize_shl_is_mul(idx_start, offset);
    }

    C::TOP_LEVEL_INDEX_RANGE().start << pte_index_bit_offset::<C>(C::NR_LEVELS())
}

/// Concrete positional end of the VA range (inclusive):
/// `(idx_range.end * 2^offset) - 1`, stated modulo `2^64` to match
/// the inclusive-end spec. The verified configs prove the pre-subtraction
/// product fits in `usize`, so the executable path can use an ordinary
/// left shift followed by `wrapping_sub(1)`.
fn pt_va_range_end<C: PageTableConfig>() -> (ret: Vaddr)
    ensures
        ret == (C::TOP_LEVEL_INDEX_RANGE().end * pow2(
            pte_index_bit_offset_spec::<C>(C::NR_LEVELS()) as nat,
        ) - 1) % 0x1_0000_0000_0000_0000int,
{
    let idx_end = C::TOP_LEVEL_INDEX_RANGE().end;
    proof {
        C::lemma_paging_consts_properties();
    }
    let offset = pte_index_bit_offset::<C>(C::NR_LEVELS());

    proof {
        crate::specs::mm::page_table::vaddr_range_proofs::lemma_pt_va_range_end_shift_facts::<C>(
            idx_end,
            offset,
        );
        vstd::bits::lemma_usize_shl_is_mul(idx_end, offset);
    }

    let shifted = idx_end << offset;
    let ret = shifted.wrapping_sub(1);

    proof {
        assert(shifted == idx_end * pow2(offset as nat));
        crate::specs::mm::page_table::vaddr_range_proofs::lemma_pt_va_range_end_wrapping_sub::<C>(
            idx_end,
            offset,
            shifted,
            ret,
        );
    }
    ret
}

fn sign_bit_of_va<C: PageTableConfig>(va: Vaddr) -> (ret: bool)
    ensures
        ret == ((va as int / pow2((C::ADDRESS_WIDTH() - 1) as nat) as int) % 2 == 1),
{
    proof {
        C::lemma_paging_consts_properties();
        C::lemma_page_table_config_constant_properties();
        vstd::bits::lemma_usize_shr_is_div(va, (C::ADDRESS_WIDTH() - 1) as usize);
        vstd::bits::lemma_usize_low_bits_mask_is_mod(va >> (C::ADDRESS_WIDTH() - 1), 1);
        vstd::bits::lemma_low_bits_mask_values();
        vstd::arithmetic::power2::lemma2_to64();
    }
    (va >> (C::ADDRESS_WIDTH() - 1)) & 1 != 0
}

/// Apply the sign-extension OR to a positional value.
///
/// For any value `va` in `[0, 2^ADDRESS_WIDTH)`, the OR with
/// `!0 ^ ((1 << ADDRESS_WIDTH) - 1)` is equivalent to adding
/// `LEADING_BITS_spec() * 2^48`, because the mask's bits and `va`'s bits are
/// disjoint.
fn apply_sign_ext<C: PageTableConfig>(va: Vaddr) -> (ret: Vaddr)
    requires
        va < pow2(C::ADDRESS_WIDTH() as nat),
        C::ADDRESS_WIDTH() < usize::BITS,
        C::LEADING_BITS_spec() * 0x1_0000_0000_0000int == 0x1_0000_0000_0000_0000int - pow2(
            C::ADDRESS_WIDTH() as nat,
        ),
    ensures
        ret == va + C::LEADING_BITS_spec() * 0x1_0000_0000_0000int,
{
    let address_width = C::ADDRESS_WIDTH();
    let low_bit = 1usize << address_width;
    proof {
        vstd::layout::unsigned_int_max_values();
        vstd::bits::lemma_usize_pow2_no_overflow(address_width as nat);
        vstd::bits::lemma_usize_shl_is_mul(1usize, address_width);
    }
    let low_mask = low_bit - 1;
    let sign_ext_mask = !0 ^ low_mask;
    let ret = va | sign_ext_mask;
    proof {
        assert(!0usize == 0xffff_ffff_ffff_ffffusize) by (compute_only);
        assert(sign_ext_mask == usize::MAX - low_mask) by (bit_vector)
            requires
                sign_ext_mask == (!0usize ^ low_mask),
                !0usize == 0xffff_ffff_ffff_ffffusize,
                usize::MAX == 0xffff_ffff_ffff_ffffusize,
        ;
        assert(pow2(64) == 0x1_0000_0000_0000_0000nat) by {
            vstd::arithmetic::power2::lemma2_to64();
        };
        assert(sign_ext_mask == 0x1_0000_0000_0000_0000int - pow2(address_width as nat));
        assert(sign_ext_mask == C::LEADING_BITS_spec() * 0x1_0000_0000_0000int);

        assert((va & sign_ext_mask) == 0usize) by (bit_vector)
            requires
                address_width < usize::BITS,
                low_bit == 1usize << address_width,
                low_mask == low_bit - 1,
                sign_ext_mask == !0usize ^ low_mask,
                va < low_bit,
        ;
        assert(ret == va + sign_ext_mask) by (bit_vector)
            requires
                ret == va | sign_ext_mask,
                (va & sign_ext_mask) == 0usize,
        ;
    }
    ret
}

/// Gets the managed virtual addresses range for the page table.
///
/// Returns a [`RangeInclusive`] because the end address, when the range
/// reaches the top of the 64-bit address space (e.g. the canonical
/// high-half kernel range ending at `usize::MAX`), would overflow the
/// exclusive end of a [`Range<Vaddr>`].
#[verusfmt::skip]
fn vaddr_range<C: PageTableConfig>() -> (ret: RangeInclusive<Vaddr>)
    ensures
        ret@ == vaddr_range_spec::<C>(),
{
    let mut start = pt_va_range_start::<C>();
    let mut end = pt_va_range_end::<C>();

    proof {
        C::lemma_paging_consts_properties();
        C::lemma_page_table_config_constant_properties();
        crate::specs::mm::page_table::vaddr_range_proofs::lemma_idx_times_pow2_bound::<C>(
            start,
            end,
        );
    }

    if C::VA_SIGN_EXT() && sign_bit_of_va::<C>(pt_va_range_start::<C>()) {
        start = apply_sign_ext::<C>(start);
        end = apply_sign_ext::<C>(end);
    }
    start..=end
}

/// Checks if the given range is covered by the valid range of the page table.
fn is_valid_range<C: PageTableConfig>(r: &Range<Vaddr>) -> bool
    requires
        r.end > 0,
    returns
        is_valid_range_spec::<C>(*r),
{
    let va_range = vaddr_range::<C>();
    (r.start == 0 && r.end == 0) || (*va_range.start() <= r.start && r.end - 1 <= *va_range.end())
}

// Here are some const values that are determined by the paging constants.
/// The number of virtual address bits used to index a PTE in a page.
fn nr_pte_index_bits<C: PagingConstsTrait>() -> usize
    returns
        nr_pte_index_bits_spec::<C>(),
{
    proof {
        C::lemma_paging_consts_properties();
    }
    nr_subpage_per_huge::<C>().ilog2() as usize
}

/// The index of a VA's PTE in a page table node at the given level.
fn pte_index<C: PagingConstsTrait>(va: Vaddr, level: PagingLevel) -> (res: usize)
    requires
        1 <= level <= NR_LEVELS,
    ensures
        res == AbstractVaddr::from_vaddr(va).index[level - 1],
{
    proof {
        let offset = pte_index_bit_offset_spec::<C>(level);
        C::lemma_paging_consts_properties();
        lemma_arch_specific_consts_properties::<C>();
        assert(0 <= offset < usize::BITS) by (nonlinear_arith)
            requires
                1 <= level <= 4,
                offset == 12 + 9 * (level - 1),
        ;
        lemma2_to64();
        lemma2_to64_rest();
        vstd::bits::lemma_usize_shr_is_div(va, pte_index_bit_offset_spec::<C>(level));
        vstd::bits::lemma_low_bits_mask_values();
        vstd::bits::lemma_usize_low_bits_mask_is_mod(
            va >> pte_index_bit_offset_spec::<C>(level),
            9,
        );
    }
    (va >> pte_index_bit_offset::<C>(level)) & (nr_subpage_per_huge::<C>() - 1)
}

/// The bit offset of the entry offset part in a virtual address.
///
/// This function returns the bit offset of the least significant bit. Take
/// x86-64 as an example, the `pte_index_bit_offset(2)` should return 21, which
/// is 12 (the 4KiB in-page offset) plus 9 (index width in the level-1 table).
fn pte_index_bit_offset<C: PagingConstsTrait>(level: PagingLevel) -> usize
    requires
        1 <= level <= NR_LEVELS,
    returns
        pte_index_bit_offset_spec::<C>(level),
{
    proof {
        C::lemma_paging_consts_properties();
        lemma_arch_specific_consts_properties::<C>();
        assert(12 + 9 * (level - 1) <= 39) by (nonlinear_arith)
            requires
                1 <= level <= NR_LEVELS,
                NR_LEVELS == 4,
        ;
    }
    C::BASE_PAGE_SIZE().ilog2() as usize + nr_pte_index_bits::<C>() * (level as usize - 1)
}

/// A handle to a page table.
/// A page table can track the lifetime of the mapped physical pages.
pub struct PageTable<C: PageTableConfig> {
    pub root: PageTableNode<C>,
}

/*
impl PageTable<UserPtConfig> {
    pub fn activate(&self) {
        // SAFETY: The user mode page table is safe to activate since the kernel
        // mappings are shared.
        unsafe {
            self.root.activate();
        }
    }
}*/

impl PageTable<KernelPtConfig> {
    /// Create a new kernel page table.
    #[verifier::external_body]
    pub(crate) fn new_kernel_page_table() -> Self {
        unimplemented!()/*        let kpt = Self::empty();

        // Make shared the page tables mapped by the root table in the kernel space.
        {
        let preempt_guard = disable_preempt();
        let mut root_node = kpt.root.borrow().lock(&preempt_guard);

        for i in KernelPtConfig::TOP_LEVEL_INDEX_RANGE {
            let mut root_entry = root_node.entry(i);
            let _ = root_entry.alloc_if_none(&preempt_guard).unwrap();
            }
        }

        kpt*/

    }

    /// Panic condition for [`Self::create_user_page_table`]:
    /// Some kernel root entry at index `i` in `TOP_LEVEL_INDEX_RANGE` is
    /// not a page table node (i.e., is absent or maps a huge frame).
    pub open spec fn create_user_pt_panic_condition(root_owner: NodeOwner<KernelPtConfig>) -> bool {
        exists|i: usize|
            #![trigger root_owner.children_perm.value()[i as int]]
            KernelPtConfig::TOP_LEVEL_INDEX_RANGE().start <= i
                < KernelPtConfig::TOP_LEVEL_INDEX_RANGE().end && {
                let pte = root_owner.children_perm.value()[i as int];
                ||| !pte.is_present()
                ||| pte.is_last(root_owner.level)
            }
    }

    /// Create a new user page table.
    ///
    /// This should be the only way to create the user page table, that is to
    /// duplicate the kernel page table with all the kernel mappings shared.
    #[verus_spec(r =>
        with Tracked(kernel_owner): Tracked<&PageTableOwner<KernelPtConfig>>,
            Tracked(regions): Tracked<&mut MetaRegionOwners>,
            Tracked(guards): Tracked<&mut Guards<'rcu>>,
        requires
            kernel_owner.inv(),
            old(regions).inv(),
            kernel_owner.0.value().is_node(),
            !Self::create_user_pt_panic_condition(kernel_owner.0.value().node()),
            // The kernel page table's root frame matches the tracked owner.
            self.root.ptr.addr() == kernel_owner.0.value().node().meta_vaddr(),
            // The kernel root entry is sound with respect to the meta regions.
            kernel_owner.0.value().metaregion_sound(*old(regions)),
            // The whole kernel page-table tree is sound: every entry's metaregion
            // bookkeeping matches `old(regions)`. Needed to derive each child's
            // soundness inside the loop body.
            kernel_owner.metaregion_sound(*old(regions)),
            // The kernel root is not currently locked.
            old(guards).unlocked(kernel_owner.0.value().node().meta_vaddr()),
        ensures
            final(regions).inv(),
    )]
    pub(in crate::mm) fn create_user_page_table<'rcu, G: InAtomicMode + 'static>(
        &'static self,
    ) -> PageTable<UserPtConfig> {
        let preempt_guard: &'rcu G = disable_preempt::<G>();

        proof_decl! {
            let tracked mut new_pt_owner: Option<PageTableOwner<UserPtConfig>> = None;
        }
        let ghost regions_before_alloc = *regions;
        let new_pt: PageTable<UserPtConfig> = (
        #[verus_spec(with Tracked(&mut new_pt_owner), Tracked(regions), Tracked(guards))]
        PageTable::empty_with_owner());
        let new_root = new_pt.root;
        // Capture new_idx as a ghost BEFORE the tracked_take below empties new_pt_owner.
        let ghost new_idx_g: int = crate::specs::mm::frame::mapping::frame_to_index(
            new_pt_owner@.unwrap().0.value().meta_slot_paddr().unwrap(),
        );
        let ghost new_pt_owner_snap = new_pt_owner@.unwrap();
        proof {
            let kern_idx = crate::specs::mm::frame::mapping::frame_to_index(
                kernel_owner.0.value().meta_slot_paddr().unwrap(),
            );
            let new_idx = new_idx_g;
            crate::specs::mm::page_table::node::entry_owners::EntryOwner::<
                KernelPtConfig,
            >::lemma_active_entry_not_in_free_pool(
                kernel_owner.0.value(),
                regions_before_alloc,
                new_idx,
            );
            assert(kern_idx != new_idx);
            assert(regions.slot_owners[kern_idx] == regions_before_alloc.slot_owners[kern_idx]);
            assert(kernel_owner.metaregion_sound(*regions));
            assert(!regions.contains(new_idx));
        }

        proof_decl! {
            let tracked root_owner: &NodeOwner<KernelPtConfig>
                = kernel_owner.0.tracked_borrow_value().tracked_borrow_node();
            let tracked mut new_pt_owner_val: PageTableOwner<UserPtConfig>
                = new_pt_owner.tracked_take();
            let tracked mut new_node_owner: NodeOwner<UserPtConfig> = {
                let tracked new_pt_value = new_pt_owner_val.0.tracked_borrow_mut_value();
                new_pt_value.tracked_take_node()
            };
            let tracked mut entry_owner: &EntryOwner<KernelPtConfig>;
        }

        // Discharge borrow/lock preconditions for the kernel root from
        // kernel_owner.inv() + metaregion_sound + guards unlocked.
        proof {
            assert(kernel_owner.0.value().is_node());
            assert(kernel_owner.0.value().metaregion_sound(*regions));
        }
        let ghost regions_before_self_borrow: MetaRegionOwners = *regions;
        let mut root_node = {
            #[verus_spec(with Tracked(regions))]
            let root_ref = self.root.borrow();
            #[verus_spec(with Tracked(root_owner), Tracked(guards))]
            root_ref.lock(preempt_guard)
        };
        let ghost regions_after_kroot_borrow: MetaRegionOwners = *regions;
        let mut new_node: PageTableGuard<'rcu, UserPtConfig> = {
            #[verus_spec(with Tracked(regions))]
            let new_ref = new_root.borrow();
            #[verus_spec(with Tracked(&new_node_owner), Tracked(guards))]
            new_ref.lock(preempt_guard)
        };
        proof {
            let kern_idx = crate::specs::mm::frame::mapping::frame_to_index(
                kernel_owner.0.value().meta_slot_paddr().unwrap(),
            );
            assert(regions_before_self_borrow.slot_owners
                == regions_after_kroot_borrow.slot_owners);
            assert forall|k: int|
                regions_before_self_borrow.contains(k) implies regions_before_self_borrow.slots[k]
                == #[trigger] regions_after_kroot_borrow.slots[k] by {
                if k == kern_idx {
                    crate::specs::mm::page_table::node::entry_owners::EntryOwner::<
                        KernelPtConfig,
                    >::lemma_active_entry_not_in_free_pool(
                        kernel_owner.0.value(),
                        regions_before_self_borrow,
                        k,
                    );
                }
            };
            kernel_owner.metaregion_sound_preserved_slot_owners_eq(
                regions_before_self_borrow,
                regions_after_kroot_borrow,
            );

            let new_idx = new_idx_g;
            assert(regions_before_alloc.contains(new_idx));
            assert(kern_idx != new_idx) by {
                crate::specs::mm::page_table::node::entry_owners::EntryOwner::<
                    KernelPtConfig,
                >::lemma_active_entry_not_in_free_pool(
                    kernel_owner.0.value(),
                    regions_before_alloc,
                    new_idx,
                );
            };

            assert(!regions_before_self_borrow.contains(new_idx));
            assert(!regions_after_kroot_borrow.contains(new_idx));
            assert forall|k: int|
                regions_after_kroot_borrow.contains(k) implies regions_after_kroot_borrow.slots[k]
                == #[trigger] regions.slots[k] by {
                if k != new_idx {
                    // borrow preserves slots[k] at k != self.index() == new_idx
                }
            };
            assert(kernel_owner.metaregion_sound(regions_before_alloc));

            kernel_owner.0.lemma_subtree_satisfies_implies(
                kernel_owner.0.value().path,
                |
                    e: crate::specs::mm::page_table::node::entry_owners::EntryOwner<KernelPtConfig>,
                    p: vstd_extra::ghost_tree::TreePath<NR_ENTRIES>,
                |
                    e.is_frame() && e.parent_level > 1 ==> {
                        let pa = e.frame().mapped_pa;
                        let nr_pages = page_size(e.parent_level) / PAGE_SIZE;
                        forall|j: usize|
                            0 < j < nr_pages ==> {
                                let sub_idx =
                                    #[trigger] crate::specs::mm::frame::mapping::frame_to_index(
                                    (pa + j * PAGE_SIZE) as usize,
                                );
                                sub_idx != new_idx
                            }
                    },
                |
                    e: crate::specs::mm::page_table::node::entry_owners::EntryOwner<KernelPtConfig>,
                    p: vstd_extra::ghost_tree::TreePath<NR_ENTRIES>,
                |
                    e.is_frame() && e.parent_level > 1 ==> {
                        let pa = e.frame().mapped_pa;
                        let nr_pages = page_size(e.parent_level) / PAGE_SIZE;
                        forall|j: usize|
                            0 < j < nr_pages ==> {
                                let sub_idx =
                                    #[trigger] crate::specs::mm::frame::mapping::frame_to_index(
                                    (pa + j * PAGE_SIZE) as usize,
                                );
                                sub_idx != new_idx || (regions.contains(sub_idx)
                                    && regions.slot_owners[sub_idx].ref_count() != REF_COUNT_UNUSED
                                    && regions.slot_owners[sub_idx].ref_count() > 0
                                    && regions.slot_owners[sub_idx].ref_count() <= REF_COUNT_MAX)
                            }
                    },
            );
            kernel_owner.metaregion_sound_preserved_one_slot_changed(
                regions_after_kroot_borrow,
                *regions,
                new_idx,
            );
        }
        let mut i: usize = KernelPtConfig::TOP_LEVEL_INDEX_RANGE().start;
        while i < KernelPtConfig::TOP_LEVEL_INDEX_RANGE().end
            invariant
                kernel_owner.inv(),
                kernel_owner.0.value().is_node(),
                regions.inv(),
                !Self::create_user_pt_panic_condition(kernel_owner.0.value().node()),
                i <= KernelPtConfig::TOP_LEVEL_INDEX_RANGE().end,
                KernelPtConfig::TOP_LEVEL_INDEX_RANGE().start <= i,
                // Lock postcondition for the kernel root.
                *root_owner == kernel_owner.0.value().node(),
                root_owner.relate_guard(root_node),
                // Tree-wide soundness of the kernel page table.
                kernel_owner.metaregion_sound(*regions),
                // The new node owner's invariants and guard relation.
                new_node_owner.inv(),
                new_node_owner.relate_guard(new_node),
                regions.contains(new_node_owner.slot_index),
            decreases KernelPtConfig::TOP_LEVEL_INDEX_RANGE().end - i,
        {
            proof {
                let kern_node = kernel_owner.0.value().node();
                assert forall|j: usize|
                    #![trigger kern_node.children_perm.value()[j as int]]
                    KernelPtConfig::TOP_LEVEL_INDEX_RANGE().start <= j
                        < KernelPtConfig::TOP_LEVEL_INDEX_RANGE().end implies {
                    let pte = kern_node.children_perm.value()[j as int];
                    pte.is_present() && !pte.is_last(kern_node.level)
                } by {
                    let pte = kern_node.children_perm.value()[j as int];
                    if !pte.is_present() || pte.is_last(kern_node.level) {
                        assert(Self::create_user_pt_panic_condition(kern_node));
                    }
                }

                kernel_owner.pt_inv_unroll(i as int);
                let tracked child_subtree: &OwnerSubtree<KernelPtConfig> =
                    kernel_owner.0.tracked_borrow_child(i as int);
                entry_owner = child_subtree.tracked_borrow_value();
                let kern_node = kernel_owner.0.value().node();
                assert(entry_owner.match_pte(
                    kern_node.children_perm.value()[i as int],
                    entry_owner.parent_level,
                ));
                assert(entry_owner.parent_level == kern_node.level);
                assert(child_subtree.inv());
                assert(entry_owner.inv());
                assert(root_owner.relate_guard(root_node));

                kernel_owner.0.lemma_subtree_satisfies_unroll_once(
                    kernel_owner.0.value().path,
                    PageTableOwner::<KernelPtConfig>::metaregion_sound_pred(*regions),
                    i as int,
                );
                assert(child_subtree.subtree_satisfies(
                    kernel_owner.0.value().path.push_tail(i as int),
                    PageTableOwner::<KernelPtConfig>::metaregion_sound_pred(*regions),
                ));
                assert(entry_owner.metaregion_sound(*regions));
            }

            #[verus_spec(with Tracked(root_owner), Tracked(entry_owner), Tracked(&*regions))]
            let root_entry = root_node.entry(i);
            let ghost pre_to_ref_regions: MetaRegionOwners = *regions;
            #[verus_spec(with Tracked(entry_owner), Tracked(root_owner), Tracked(regions))]
            let child = root_entry.to_ref();

            proof {
                let kern_node = kernel_owner.0.value().node();
                let pte = kern_node.children_perm.value()[i as int];

                assert(pte.is_present() && !pte.is_last(kern_node.level)) by {
                    if !pte.is_present() || pte.is_last(kern_node.level) {
                        assert(KernelPtConfig::TOP_LEVEL_INDEX_RANGE().start <= i
                            < KernelPtConfig::TOP_LEVEL_INDEX_RANGE().end);
                        assert(exists|j: usize|
                            KernelPtConfig::TOP_LEVEL_INDEX_RANGE().start <= j
                                < KernelPtConfig::TOP_LEVEL_INDEX_RANGE().end && {
                                let p = #[trigger] kern_node.children_perm.value()[j as int];
                                ||| !p.is_present()
                                ||| p.is_last(kern_node.level)
                            });
                        assert(Self::create_user_pt_panic_condition(kern_node));
                    }
                }
                // entry_owner.match_pte(pte, parent_level) + (present && !is_last)
                // ⟹ entry_owner.is_node().
                assert(entry_owner.is_node());
                // ChildRef::invariants(entry_owner, regions) gives child.wf(entry_owner).
                // For the Frame and None variants, wf requires is_frame() or is_absent(),
                // contradicting is_node(). Hence child must be PageTable.
                assert(child is PageTable);
                // to_ref's borrow_paddr preserves slot_owners exactly and only
                // grows `slots` (existing keys preserved). Use the tree-wide
                // preservation lemma.
                kernel_owner.metaregion_sound_preserved_slot_owners_eq(
                    pre_to_ref_regions,
                    *regions,
                );
            }
            let pt = match child {
                ChildRef::PageTable(pt) => pt,
                _ => vstd::pervasive::unreached(),
            };

            let ghost entry_node_slot_idx = entry_owner.tracked_borrow_node().slot_index;
            let tracked entry_node_slot_perm = regions.slots.tracked_borrow(entry_node_slot_idx);
            #[verus_spec(with Tracked(entry_node_slot_perm))]
            let pt_addr = pt.start_paddr();
            let pte = PageTableEntry::new_pt(pt_addr);

            proof {
                assert(regions.contains(new_node_owner.slot_index));
            }
            unsafe {
                #[verus_spec(with Tracked(&mut new_node_owner), Tracked(&*regions))]
                new_node.write_pte(i, pte)
            };

            i = i + 1;
        }

        PageTable::<UserPtConfig> { root: new_root }
    }/*
    /// Protect the given virtual address range in the kernel page table.
    ///
    /// This method flushes the TLB entries when doing protection.
    ///
    /// # Safety
    ///
    /// The caller must ensure that the protection operation does not affect
    /// the memory safety of the kernel.
    pub unsafe fn protect_flush_tlb(
        &self,
        vaddr: &Range<Vaddr>,
        mut op: impl FnMut(&mut PageProperty),
    ) -> Result<(), PageTableError> {
        let preempt_guard = disable_preempt();
        let mut cursor = CursorMut::new(self, &preempt_guard, vaddr)?;
        // SAFETY: The safety is upheld by the caller.
        while let Some(range) =
            unsafe { cursor.protect_next(vaddr.end - cursor.virt_addr(), &mut op) }
        {
            crate::arch::mm::tlb_flush_addr(range.start);
        }
        Ok(())
    }*/

}

#[verus_verify]
impl<C: PageTableConfig> PageTable<C> {
    /// Relates this executable page-table handle to its tracked ownership tree.
    pub open spec fn relates_owner(
        &self,
        owner: PageTableOwner<C>,
        regions: MetaRegionOwners,
    ) -> bool {
        &&& owner.inv()
        &&& self.root.ptr.addr() == owner.0.value().node().meta_vaddr()
        &&& owner.metaregion_sound(regions)
    }

    /// Create a new empty page table.
    ///
    /// Useful for the IOMMU page tables only.
    #[verifier::external_body]
    pub fn empty() -> Self {
        unimplemented!()
    }

    /// Create a new empty page table together with its tracked ownership.
    #[verifier::external_body]
    #[verus_spec(r =>
        with Tracked(owner): Tracked<&mut Option<PageTableOwner<C>>>,
            Tracked(regions): Tracked<&mut MetaRegionOwners>,
            Tracked(guards): Tracked<&mut Guards<'rcu>>,
        requires
            old(regions).inv(),
        ensures
            final(owner)@ is Some,
            final(owner)@->0.inv(),
            (final(owner)@->0).0.value().is_node(),
            (final(owner)@->0).0.value().is_node(),
            r.root.ptr.addr() == (final(owner)@->0).0.value().node().meta_vaddr(),
            (final(owner)@->0).0.value().metaregion_sound(*final(regions)),
            final(regions).inv(),
            final(guards).unlocked((final(owner)@->0).0.value().node().meta_vaddr()),
            // Allocating a fresh node does not change the lock set, so any node
            // that was (un)locked before remains so.
            final(guards).guards == old(guards).guards,
            // The newly allocated slot was in the free pool before the call.
            old(regions).contains(
                crate::specs::mm::frame::mapping::frame_to_index(
                    (final(owner)@->0).0.value().meta_slot_paddr()->0)),
            // After the alloc, the slot is removed from the free pool (now owned
            // by the new pt's NodeOwner).
            !final(regions).contains(
                crate::specs::mm::frame::mapping::frame_to_index(
                    (final(owner)@->0).0.value().meta_slot_paddr()->0)),
            // Other slots and lock state are preserved.
            forall |i: int| #![trigger final(regions).slot_owners[i]]
                i != crate::specs::mm::frame::mapping::frame_to_index(
                    (final(owner)@->0).0.value().meta_slot_paddr()->0)
                ==> final(regions).slot_owners[i] == old(regions).slot_owners[i],
            forall |a: usize| old(guards).lock_held(a) ==> final(guards).lock_held(a),
            forall |idx: int| #![trigger final(regions).slot_owners[idx].paths_in_pt]
                final(regions).slot_owners[idx].paths_in_pt
                    == old(regions).slot_owners[idx].paths_in_pt,
            // Allocation preserves the soundness of the kernel page-table tree:
            // a fresh allocation cannot collide with any active node or frame entry
            // (the allocator returns a slot that wasn't in use). Stated as a
            // postcondition because deriving it requires a freshness axiom on the
            // underlying frame allocator.
            forall |kt: PageTableOwner<KernelPtConfig>|
                #![trigger kt.metaregion_sound(*final(regions))]
                kt.inv() && kt.metaregion_sound(*old(regions))
                ==> kt.metaregion_sound(*final(regions)),
            // Freshness: the new PT's slot index is not used (as a primary slot
            // or huge-frame sub-page slot) by any entry in any KernelPtConfig PT
            // tree that was sound before the alloc. Used to discharge the borrow
            // step that mutates `slot_owners[new_idx]`.
            forall |kt: PageTableOwner<KernelPtConfig>|
                #![trigger kt.metaregion_sound(*old(regions))]
                kt.inv() && kt.metaregion_sound(*old(regions)) ==>
                kt.0.subtree_satisfies(
                    kt.0.value().path,
                    |e: crate::specs::mm::page_table::node::entry_owners::EntryOwner<KernelPtConfig>,
                     p: vstd_extra::ghost_tree::TreePath<NR_ENTRIES>|
                        e.meta_slot_paddr() is Some
                            ==> crate::specs::mm::frame::mapping::frame_to_index(
                                e.meta_slot_paddr()->0) !=
                                crate::specs::mm::frame::mapping::frame_to_index(
                                    (final(owner)@->0).0.value().meta_slot_paddr()->0),
                ),
            // Sub-page freshness: for any huge frame entry in any pre-existing
            // sound KernelPtConfig tree, the new PT's slot index isn't a sub-page
            // slot of the huge frame either. Same allocator-freshness rationale.
            forall |kt: PageTableOwner<KernelPtConfig>|
                #![trigger kt.metaregion_sound(*old(regions))]
                kt.inv() && kt.metaregion_sound(*old(regions)) ==>
                kt.0.subtree_satisfies(
                    kt.0.value().path,
                    |e: crate::specs::mm::page_table::node::entry_owners::EntryOwner<KernelPtConfig>,
                     p: vstd_extra::ghost_tree::TreePath<NR_ENTRIES>|
                        e.is_frame() && e.parent_level > 1 ==> {
                            let pa = e.frame().mapped_pa;
                            let nr_pages = page_size(
                                e.parent_level) / PAGE_SIZE;
                            forall |j: usize| 0 < j < nr_pages ==> {
                                let sub_idx =
                                    #[trigger] crate::specs::mm::frame::mapping::frame_to_index(
                                        (pa + j * PAGE_SIZE) as usize);
                                sub_idx != crate::specs::mm::frame::mapping::frame_to_index(
                                    (final(owner)@->0).0.value().meta_slot_paddr()->0)
                            }
                        },
                ),
    )]
    pub fn empty_with_owner<'rcu>() -> Self {
        unimplemented!()
    }

    #[verifier::external_body]
    pub(in crate::mm) unsafe fn first_activate_unchecked(&self) {
        unimplemented!()
        // SAFETY: The safety is upheld by the caller.
        //        unsafe { self.root.first_activate() };

    }

    pub uninterp spec fn root_paddr_spec(&self) -> Paddr;

    /// The physical address of the root page table.
    ///
    /// Obtaining the physical address of the root page table is safe, however, using it or
    /// providing it to the hardware will be unsafe since the page table node may be dropped,
    /// resulting in UAF.
    #[verifier::external_body]
    #[verifier::when_used_as_spec(root_paddr_spec)]
    pub fn root_paddr(&self) -> (r: Paddr)
        returns
            self.root_paddr_spec(),
    {
        unimplemented!()
        //        self.root.start_paddr()

    }

    /// Query about the mapping of a single byte at the given virtual address.
    ///
    /// Note that this function may fail reflect an accurate result if there are
    /// cursors concurrently accessing the same virtual address range, just like what
    /// happens for the hardware MMU walk.
    #[cfg(ktest)]
    pub fn page_walk(&self, vaddr: Vaddr) -> Option<(Paddr, PageProperty)> {
        // SAFETY: The root node is a valid page table node so the address is valid.
        unsafe { page_walk::<C>(self.root_paddr(), vaddr) }
    }

    /// Create a new cursor exclusively accessing the virtual address range for mapping.
    ///
    /// If another cursor is already accessing the range, the new cursor may wait until the
    /// previous cursor is dropped.
    #[verus_spec(r =>
        with Tracked(owner): Tracked<PageTableOwner<C>>,
            Ghost(root_guard): Ghost<PageTableGuard<'rcu, C>>,
            Tracked(regions): Tracked<&mut MetaRegionOwners>,
            Tracked(guards): Tracked<&mut Guards<'rcu>>
        requires
            self.relates_owner(owner, *old(regions)),
            owner.0.value().node().relate_guard(root_guard),
            // Per-config tightening; see `Cursor::new`.
            0 < va.end <= C::LOCKED_END_BOUND_spec(),
        ensures
            Cursor::<C, G>::cursor_new_success_conditions(*va) ==> {
                &&& r is Ok
                &&& r.unwrap().0.0.invariants(*r.unwrap().1, *final(regions), *final(guards))
                &&& r.unwrap().1.in_locked_range()
                &&& r.unwrap().0.0.level == r.unwrap().0.0.guard_level
                &&& r.unwrap().0.0.guard_level == NR_LEVELS as PagingLevel
                &&& r.unwrap().0.0.va < r.unwrap().0.0.barrier_va.end
                &&& r.unwrap().0.0.va == va.start
                &&& r.unwrap().0.0.barrier_va == *va
            },
            !Cursor::<C, G>::cursor_new_success_conditions(*va) ==> r is Err,
            forall |item: C::Item| #![trigger CursorMut::<'rcu, C, G>::item_not_mapped(item, *old(regions))]
                CursorMut::<'rcu, C, G>::item_not_mapped(item, *old(regions)) ==>
                CursorMut::<'rcu, C, G>::item_not_mapped(item, *final(regions)),
            // CursorMut::new inherits Cursor::new's weakened preservation:
            // PT-node allocations come from UNUSED slots, so any slot that
            // was already in use keeps its paths_in_pt.
            forall |idx: int| #![trigger final(regions).slot_owners[idx].paths_in_pt]
                old(regions).slot_owners[idx].ref_count()
                    != REF_COUNT_UNUSED
                ==> final(regions).slot_owners[idx].paths_in_pt
                        == old(regions).slot_owners[idx].paths_in_pt,
            forall|idx: int| #![trigger final(regions).slot_owners[idx]]
                old(regions).contains(idx)
                && old(regions).slot_owners[idx].ref_count()
                    != REF_COUNT_UNUSED
                ==> final(regions).slot_owners[idx].ref_count()
                        == old(regions).slot_owners[idx].ref_count()
                    && final(regions).slot_owners[idx].usage
                        == old(regions).slot_owners[idx].usage,
    )]
    pub fn cursor_mut<'rcu, G: InAtomicMode>(
        &'rcu self,
        guard: &'rcu G,
        va: &Range<Vaddr>,
    ) -> Result<(CursorMut<'rcu, C, G>, Tracked<CursorOwner<'rcu, C>>), PageTableError> {
        #[verus_spec(with Tracked(owner), Ghost(root_guard), Tracked(regions), Tracked(guards))]
        CursorMut::new(self, guard, va)
    }

    /// Create a new cursor exclusively accessing the virtual address range for querying.
    ///
    /// If another cursor is already accessing the range, the new cursor may wait until the
    /// previous cursor is dropped. The modification to the mapping by the cursor may also
    /// block or be overridden by the mapping of another cursor.
    #[verus_spec(r =>
        with Tracked(owner): Tracked<PageTableOwner<C>>,
            Ghost(root_guard): Ghost<PageTableGuard<'rcu, C>>,
            Tracked(regions): Tracked<&mut MetaRegionOwners>,
            Tracked(guards): Tracked<&mut Guards<'rcu>>
        requires
            self.relates_owner(owner, *old(regions)),
            owner.0.value().node().relate_guard(root_guard),
            // Per-config tightening; see `Cursor::new`.
            0 < va.end <= C::LOCKED_END_BOUND_spec(),
        ensures
            Cursor::<C, G>::cursor_new_success_conditions(*va) ==> {
                &&& r is Ok
                &&& r.unwrap().0.invariants(*r.unwrap().1, *final(regions), *final(guards))
                &&& r.unwrap().1.in_locked_range()
                &&& r.unwrap().0.level == r.unwrap().0.guard_level
                &&& r.unwrap().0.va < r.unwrap().0.barrier_va.end
                &&& r.unwrap().0.va == va.start
                &&& r.unwrap().0.barrier_va == *va
                &&& r.unwrap().1@.as_page_table_owner() == owner
                &&& r.unwrap().1@.continuations[3].path() == owner.0.value().path
            },
            !Cursor::<C, G>::cursor_new_success_conditions(*va) ==> r is Err,
            forall|idx: int| #![trigger final(regions).slot_owners[idx].paths_in_pt]
                old(regions).slot_owners[idx].ref_count()
                    != REF_COUNT_UNUSED
                ==> final(regions).slot_owners[idx].paths_in_pt
                        == old(regions).slot_owners[idx].paths_in_pt,
            // Non-saturation preservation.
            (forall |i: int| #![trigger old(regions).slot_owners[i]]
                old(regions).contains(i)
                && old(regions).slot_owners[i].ref_count()
                    != REF_COUNT_UNUSED
                ==> old(regions).slot_owners[i].ref_count() + 1
                    < REF_COUNT_MAX)
            ==>
            (forall |i: int| #![trigger final(regions).slot_owners[i]]
                final(regions).contains(i)
                && final(regions).slot_owners[i].ref_count()
                    != REF_COUNT_UNUSED
                ==> final(regions).slot_owners[i].ref_count() + 1
                    < REF_COUNT_MAX),
            // Saturated-slot bridge (relayed from `Cursor::new`):
            // a slot at `>= REF_COUNT_MAX` before iff after, with the same
            // value. Used by `KVirtArea::query` to bridge inner-cursor
            // saturation back to the caller's snapshot.
            forall|idx: int| #![trigger final(regions).slot_owners[idx].ref_count()]
                final(regions).slot_owners[idx].ref_count()
                    >= REF_COUNT_MAX
                ==> old(regions).slot_owners[idx].ref_count()
                        == final(regions).slot_owners[idx].ref_count(),
            forall|idx: int| #![trigger old(regions).slot_owners[idx].ref_count()]
                old(regions).slot_owners[idx].ref_count()
                    >= REF_COUNT_MAX
                ==> final(regions).slot_owners[idx].ref_count()
                        == old(regions).slot_owners[idx].ref_count(),
    )]
    pub fn cursor<'rcu, G: InAtomicMode>(&'rcu self, guard: &'rcu G, va: &Range<Vaddr>) -> Result<
        (Cursor<'rcu, C, G>, Tracked<CursorOwner<'rcu, C>>),
        PageTableError,
    > {
        #[verus_spec(with Tracked(owner), Ghost(root_guard), Tracked(regions), Tracked(guards))]
        Cursor::new(self, guard, va)
    }/*
    /// Create a new reference to the same page table.
    /// The caller must ensure that the kernel page table is not copied.
    /// This is only useful for IOMMU page tables. Think twice before using it in other cases.
    pub unsafe fn shallow_copy(&self) -> Self {
        PageTable {
            root: self.root.clone(),
        }
    }
    */

}

/// A software emulation of the MMU address translation process.
///
/// This method returns the physical address of the given virtual address and
/// the page property if a valid mapping exists for the given virtual address.
///
/// # Safety
///
/// The caller must ensure that the `root_paddr` is a pointer to a valid root
/// page table node.
///
/// # Notes on the page table use-after-free problem
///
/// Neither the hardware MMU nor the software page walk method acquires the page
/// table locks while reading. They can enter a to-be-recycled page table node
/// and read the page table entries after the node is recycled and reused.
///
/// For the hardware MMU page walk, we mitigate this problem by dropping the page
/// table nodes only after the TLBs have been flushed on all the CPUs that
/// activate the page table.
///
/// For the software page walk, we only need to disable preemption at the beginning
/// since the page table nodes won't be recycled in the RCU critical section.
#[cfg(ktest)]
pub(super) unsafe fn page_walk<C: PageTableConfig>(root_paddr: Paddr, vaddr: Vaddr) -> Option<
    (Paddr, PageProperty),
> {
    use super::paddr_to_vaddr;

    let _rcu_guard = disable_preempt();

    let mut pt_addr = paddr_to_vaddr(root_paddr);
    #[verusfmt::skip]
    for cur_level in (1..= C::NR_LEVELS()).rev() {
        let offset = pte_index::<C>(vaddr, cur_level);
        // SAFETY:
        //  - The page table node is alive because (1) the root node is alive and
        //    (2) all child nodes cannot be recycled because we're in the RCU critical section.
        //  - The index is inside the bound, so the page table entry is valid.
        //  - All page table entries are aligned and accessed with atomic operations only.
        let cur_pte = unsafe { load_pte((pt_addr as *mut C::E).add(offset), Ordering::Acquire) };

        if !cur_pte.is_present() {
            return None;
        }
        if cur_pte.is_last(cur_level) {
            debug_assert!(cur_level <= C::HIGHEST_TRANSLATION_LEVEL);
            return Some(
                (cur_pte.paddr() + (vaddr & (page_size::<C>(cur_level) - 1)), cur_pte.prop()),
            );
        }
        pt_addr = paddr_to_vaddr(cur_pte.paddr());
    }

    unreachable!("All present PTEs at the level 1 must be last-level PTEs");
}

/// A trait that abstracts architecture-specific page table entries (PTEs).
///
/// Note that a default PTE should be a PTE that points to nothing.
pub trait PageTableEntryTrait:
    Clone + Copy + Debug + Default + Sized + Pod + PodOnce + Send + Sync + 'static {
    spec fn new_absent_spec() -> Self;

    /// Create a set of new invalid page table flags that indicates an absent page.
    ///
    /// Note that currently the implementation requires an all zero PTE to be an absent PTE.
    #[verifier(when_used_as_spec(new_absent_spec))]
    fn new_absent() -> (res: Self)
        ensures
            valid_frame_paddr(res.paddr()),
            !res.is_present(),
        returns
            Self::new_absent(),
    ;

    spec fn is_present_spec(&self) -> bool;

    /// Returns if the PTE points to something.
    ///
    /// For PTEs created by [`Self::new_absent`], this method should return
    /// false. For PTEs created by [`Self::new_page`] or [`Self::new_pt`]
    /// and modified with [`Self::set_prop`], this method should return true.
    #[verifier::when_used_as_spec(is_present_spec)]
    fn is_present(&self) -> bool
        returns
            self.is_present_spec(),
    ;

    spec fn new_page_spec(paddr: Paddr, level: PagingLevel, prop: PageProperty) -> Self;

    /// The preconditions for creating a new page-mapping PTE.
    spec fn new_page_req(paddr: Paddr, level: PagingLevel, prop: PageProperty) -> bool;

    /// Creates a new PTE that maps to a page.
    #[verifier::when_used_as_spec(new_page_spec)]
    fn new_page(paddr: Paddr, level: PagingLevel, prop: PageProperty) -> (res: Self)
        requires
            paddr < MAX_PADDR,
            Self::new_page_req(paddr, level, prop),
        ensures
            res.paddr() == paddr & !((PAGE_SIZE - 1) as usize),
            paddr % PAGE_SIZE == 0 ==> res.paddr() == paddr,
            valid_frame_paddr(res.paddr()),
            res.is_present(),
            res.is_last(level),
            res.prop() == prop,
        returns
            Self::new_page(paddr, level, prop),
    ;

    spec fn new_pt_spec(paddr: Paddr) -> Self;

    /// Create a new PTE that map to a child page table.
    #[verifier::when_used_as_spec(new_pt_spec)]
    fn new_pt(paddr: Paddr) -> (res: Self)
        requires
            paddr < MAX_PADDR,
        ensures
            res.paddr() == paddr & !((PAGE_SIZE - 1) as usize),
            paddr % PAGE_SIZE == 0 ==> res.paddr() == paddr,
            valid_frame_paddr(res.paddr()),
            res.is_present(),
            forall|level: PagingLevel| !res.is_last(level),
        returns
            Self::new_pt(paddr),
    ;

    /// Returns the physical address from the PTE.
    ///
    /// The physical address recorded in the PTE is either:
    /// - the physical address of the next-level page table, or
    /// - the physical address of the page that the PTE maps to.
    spec fn paddr_spec(&self) -> Paddr;

    #[verifier::when_used_as_spec(paddr_spec)]
    fn paddr(&self) -> (res: Paddr)
        ensures
            valid_frame_paddr(res),
        returns
            self.paddr(),
    ;

    spec fn prop_spec(&self) -> PageProperty;

    #[verifier::when_used_as_spec(prop_spec)]
    fn prop(&self) -> PageProperty
        returns
            self.prop(),
    ;

    /// The preconditions for setting the page property of a PTE.
    spec fn set_prop_req(self, prop: PageProperty) -> bool;

    fn set_prop(&mut self, prop: PageProperty)
        requires
            old(self).set_prop_req(prop),
        ensures
            !old(self).is_present() ==> *old(self) == *final(self),
            old(self).is_present() ==> {
                &&& final(self).prop() == prop
                &&& final(self).paddr() == old(self).paddr()
                &&& final(self).is_present()
                &&& forall|level: PagingLevel|
                    #![trigger old(self).is_last(level)]
                    old(self).is_last(level) ==> final(self).is_last(level)
            },
    ;

    spec fn is_last_spec(&self, level: PagingLevel) -> bool;

    /// Returns if the PTE maps a page rather than a child page table.
    ///
    /// The method needs to know the level of the page table where the PTE resides,
    /// since architectures like x86-64 have a huge bit only in intermediate levels.
    #[verifier::when_used_as_spec(is_last_spec)]
    fn is_last(&self, level: PagingLevel) -> bool
        returns
            self.is_last_spec(level),
    ;

    spec fn as_usize_spec(self) -> usize;

    /// Converts the PTE into a raw `usize` value.
    #[verifier::external_body]
    #[verifier::when_used_as_spec(as_usize_spec)]
    fn as_usize(self) -> usize
        returns
            self.as_usize(),
    {
        unimplemented!()
        // const { assert!(size_of::<Self>() == size_of::<usize>()) };
        // SAFETY: `Self` is `Pod` and has the same memory representation as `usize`.
        // unsafe { transmute_unchecked(self) }

    }

    /// Converts the raw `usize` value into a PTE.
    #[verifier::external_body]
    fn from_usize(pte_raw: usize) -> Self {
        unimplemented!()
        // const { assert!(size_of::<Self>() == size_of::<usize>()) };
        // SAFETY: `Self` is `Pod` and has the same memory representation as `usize`.
        // unsafe { transmute_unchecked(pte_raw) }

    }

    /// Absent (zero) PTE has well-formed paddr for match_pte.
    proof fn lemma_page_table_entry_properties()
        ensures
            core::mem::size_of::<Self>() == core::mem::size_of::<usize>(),
            core::mem::size_of::<Self>() % core::mem::align_of::<Self>() == 0,
            core::mem::align_of::<Self>() > 0,
            valid_frame_paddr(Self::new_absent().paddr()),
            !Self::new_absent().is_present(),
            forall|level: PagingLevel|
                #![trigger Self::new_absent().is_last(level)]
                1 < level ==> !Self::new_absent().is_last(level),
            forall|paddr: Paddr, level: PagingLevel, prop: PageProperty|
                #![trigger Self::new_page(paddr, level, prop)]
                Self::new_page_req(paddr, level, prop) && (prop.cache is Writeback
                    || prop.cache is Writethrough || prop.cache is Uncacheable) ==> {
                    &&& Self::new_page(paddr, level, prop).is_present()
                    &&& (paddr < MAX_PADDR ==> Self::new_page(paddr, level, prop).paddr() == paddr
                        & !((PAGE_SIZE - 1) as usize))
                    &&& (paddr < MAX_PADDR && paddr % PAGE_SIZE == 0 ==> Self::new_page(
                        paddr,
                        level,
                        prop,
                    ).paddr() == paddr)
                    &&& Self::new_page(paddr, level, prop).prop() == prop
                    &&& Self::new_page(paddr, level, prop).is_last(level)
                },
            forall|paddr: Paddr|
                #![trigger Self::new_pt(paddr)]
                {
                    &&& Self::new_pt(paddr).is_present()
                    &&& (paddr < MAX_PADDR ==> Self::new_pt(paddr).paddr() == paddr & !((PAGE_SIZE
                        - 1) as usize))
                    &&& (paddr < MAX_PADDR && paddr % PAGE_SIZE == 0 ==> Self::new_pt(paddr).paddr()
                        == paddr)
                    &&& forall|level: PagingLevel| !Self::new_pt(paddr).is_last(level)
                },
    ;

    proof fn lemma_paddr_is_page_aligned(self)
        ensures
            self.paddr() % PAGE_SIZE == 0,
    ;
}

/// Loads a page table entry with an atomic instruction.
///
/// # Verification Design
/// ## Preconditions
/// - The pointer must be a valid pointer to the array that represents the page table node.
/// - The array must be initialized at the target index.
/// ## Postconditions
/// - The value is loaded from the array at the given index.
/// ## Safety
/// - We require the caller to provide a permission token to ensure that this function is only called on a valid array
/// and the pointer is in bounds.
/// - Like an `AtomicUsize::load` in normal Rust, this function assumes that the value being loaded is an integer
/// (and therefore can be safely cloned). We model the PTE as an abstract type, but in all actual implementations it is an
/// integer. Importantly, it does not include any data that is unsafe to duplicate.
#[verifier::external_body]
#[verus_spec(
    with Tracked(perm): Tracked<&vstd_extra::array_ptr::PointsTo<E, NR_ENTRIES>>
    requires
        perm.is_init(ptr.index as int),
        perm.addr() == ptr.addr(),
        0 <= ptr.index < NR_ENTRIES,
    returns
        perm.value()[ptr.index as int],
)]
pub unsafe fn load_pte<E: PageTableEntryTrait>(
    ptr: vstd_extra::array_ptr::ArrayPtr<E, NR_ENTRIES>,
    ordering: Ordering,
) -> (pte: E) {
    unimplemented!()
}

/// Stores a page table entry with an atomic instruction.
///
/// # Verification Design
/// We axiomatize this function as a store operation in the array that represents the page table node.
/// ## Preconditions
/// - The pointer must be a valid pointer to the array that represents the page table node.
/// - The array must be initialized so that the verifier knows that it remains initialized after the store.
/// ## Postconditions
/// - The new value is stored in the array at the given index.
/// ## Safety
/// - We require the caller to provide a permission token to ensure that this function is only called on a valid array
/// and the pointer is in bounds.
#[verifier::external_body]
#[verus_spec(
    with Tracked(perm): Tracked<&mut vstd_extra::array_ptr::PointsTo<E, NR_ENTRIES>>
    requires
        old(perm).addr() == ptr.addr(),
        0 <= ptr.index < NR_ENTRIES,
        old(perm).is_init_all(),
    ensures
        final(perm).wf(),
        final(perm).value()[ptr.index as int] == new_val,
        final(perm).value() == old(perm).value().update(ptr.index as int, new_val),
        final(perm).addr() == old(perm).addr(),
        final(perm).is_init_all(),
)]
pub unsafe fn store_pte<E: PageTableEntryTrait>(
    ptr: vstd_extra::array_ptr::ArrayPtr<E, NR_ENTRIES>,
    new_val: E,
    ordering: Ordering,
);

} // verus!