add clean_up and clean_up_with_filter

src/addr.rs

@@ -3,6 +3,7 @@
 use core::fmt;
 use core::ops::{Add, AddAssign, Sub, SubAssign};
 
+use crate::structures::paging::page_table::PageTableLevel;
 use crate::structures::paging::{PageOffset, PageTableIndex};
 use bit_field::BitField;
 
@@ -198,6 +199,12 @@ impl VirtAddr {
     pub const fn p4_index(self) -> PageTableIndex {
         PageTableIndex::new_truncate((self.0 >> 12 >> 9 >> 9 >> 9) as u16)
     }
+
+    /// Returns the 9-bit level page table index.
+    #[inline]
+    pub const fn page_table_index(self, level: PageTableLevel) -> PageTableIndex {
+        PageTableIndex::new_truncate((self.0 >> 12 >> ((level as u8 - 1) * 9)) as u16)
+    }
 }
 
 impl fmt::Debug for VirtAddr {

src/instructions/tlb.rs

@@ -72,6 +72,7 @@ impl Pcid {
 /// Invalidate the given address in the TLB using the `invpcid` instruction.
 ///
 /// ## Safety
+///
 /// This function is unsafe as it requires CPUID.(EAX=07H, ECX=0H):EBX.INVPCID to be 1.
 #[inline]
 pub unsafe fn flush_pcid(command: InvPicdCommand) {

src/registers/control.rs

@@ -301,6 +301,7 @@ mod x86_64 {
         /// Write a new P4 table address into the CR3 register.
         ///
         /// ## Safety
+        ///
         /// Changing the level 4 page table is unsafe, because it's possible to violate memory safety by
         /// changing the page mapping.
         #[inline]
@@ -311,6 +312,7 @@ mod x86_64 {
         /// Write a new P4 table address into the CR3 register.
         ///
         /// ## Safety
+        ///
         /// Changing the level 4 page table is unsafe, because it's possible to violate memory safety by
         /// changing the page mapping.
         /// [`Cr4Flags::PCID`] must be set before calling this method.
@@ -322,6 +324,7 @@ mod x86_64 {
         /// Write a new P4 table address into the CR3 register.
         ///
         /// ## Safety
+        ///
         /// Changing the level 4 page table is unsafe, because it's possible to violate memory safety by
         /// changing the page mapping.
         #[inline]
@@ -400,6 +403,7 @@ mod x86_64 {
         /// Updates CR4 flags.
         ///
         /// Preserves the value of reserved fields.
+        ///
         /// ## Safety
         ///
         /// This function is unsafe because it's possible to violate memory

src/structures/idt.rs

@@ -789,6 +789,7 @@ impl EntryOptions {
     /// This function panics if the index is not in the range 0..7.
     ///
     /// ## Safety
+    ///
     /// This function is unsafe because the caller must ensure that the passed stack index is
     /// valid and not used by other interrupts. Otherwise, memory safety violations are possible.
     #[inline]

src/structures/paging/mapper/mapped_page_table.rs

@@ -1,9 +1,9 @@
 use crate::structures::paging::{
     frame::PhysFrame,
-    frame_alloc::FrameAllocator,
+    frame_alloc::{FrameAllocator, FrameDeallocator},
     mapper::*,
-    page::{AddressNotAligned, Page, Size1GiB, Size2MiB, Size4KiB},
-    page_table::{FrameError, PageTable, PageTableEntry, PageTableFlags},
+    page::{AddressNotAligned, Page, PageRangeInclusive, Size1GiB, Size2MiB, Size4KiB},
+    page_table::{FrameError, PageTable, PageTableEntry, PageTableFlags, PageTableLevel},
 };
 
 /// A Mapper implementation that relies on a PhysAddr to VirtAddr conversion function.
@@ -584,6 +584,90 @@ impl<'a, P: PageTableFrameMapping> Translate for MappedPageTable<'a, P> {
     }
 }
 
+impl<'a, P: PageTableFrameMapping> CleanUp for MappedPageTable<'a, P> {
+    #[inline]
+    unsafe fn clean_up<D>(&mut self, frame_deallocator: &mut D)
+    where
+        D: FrameDeallocator<Size4KiB>,
+    {
+        self.clean_up_addr_range(
+            PageRangeInclusive {
+                start: Page::from_start_address(VirtAddr::new(0)).unwrap(),
+                end: Page::from_start_address(VirtAddr::new(0xffff_ffff_ffff_f000)).unwrap(),
+            },
+            frame_deallocator,
+        )
+    }
+
+    unsafe fn clean_up_addr_range<D>(
+        &mut self,
+        range: PageRangeInclusive,
+        frame_deallocator: &mut D,
+    ) where
+        D: FrameDeallocator<Size4KiB>,
+    {
+        unsafe fn clean_up<P: PageTableFrameMapping>(
+            page_table: &mut PageTable,
+            page_table_walker: &PageTableWalker<P>,
+            level: PageTableLevel,
+            range: PageRangeInclusive,
+            frame_deallocator: &mut impl FrameDeallocator<Size4KiB>,
+        ) -> bool {
+            if range.is_empty() {
+                return false;
+            }
+
+            let table_addr = range
+                .start
+                .start_address()
+                .align_down(level.table_address_space_alignment());
+
+            let start = range.start.page_table_index(level);
+            let end = range.end.page_table_index(level);
+
+            if let Some(next_level) = level.next_lower_level() {
+                let offset_per_entry = level.entry_address_space_alignment();
+                for (i, entry) in page_table
+                    .iter_mut()
+                    .enumerate()
+                    .take(usize::from(end) + 1)
+                    .skip(usize::from(start))
+                {
+                    if let Ok(page_table) = page_table_walker.next_table_mut(entry) {
+                        let start = table_addr + (offset_per_entry * (i as u64));
+                        let end = start + (offset_per_entry - 1);
+                        let start = Page::<Size4KiB>::containing_address(start);
+                        let start = start.max(range.start);
+                        let end = Page::<Size4KiB>::containing_address(end);
+                        let end = end.min(range.end);
+                        if clean_up(
+                            page_table,
+                            page_table_walker,
+                            next_level,
+                            Page::range_inclusive(start, end),
+                            frame_deallocator,
+                        ) {
+                            let frame = entry.frame().unwrap();
+                            entry.set_unused();
+                            frame_deallocator.deallocate_frame(frame);
+                        }
+                    }
+                }
+            }
+
+            page_table.iter().all(PageTableEntry::is_unused)
+        }
+
+        clean_up(
+            self.level_4_table,
+            &self.page_table_walker,
+            PageTableLevel::Four,
+            range,
+            frame_deallocator,
+        );
+    }
+}
+
 #[derive(Debug)]
 struct PageTableWalker<P: PageTableFrameMapping> {
     page_table_frame_mapping: P,

src/structures/paging/mapper/mod.rs

@@ -7,8 +7,10 @@ pub use self::offset_page_table::OffsetPageTable;
 pub use self::recursive_page_table::{InvalidPageTable, RecursivePageTable};
 
 use crate::structures::paging::{
-    frame_alloc::FrameAllocator, page_table::PageTableFlags, Page, PageSize, PhysFrame, Size1GiB,
-    Size2MiB, Size4KiB,
+    frame_alloc::{FrameAllocator, FrameDeallocator},
+    page::PageRangeInclusive,
+    page_table::PageTableFlags,
+    Page, PageSize, PhysFrame, Size1GiB, Size2MiB, Size4KiB,
 };
 use crate::{PhysAddr, VirtAddr};
 
@@ -480,3 +482,45 @@ pub enum TranslateError {
 }
 
 static _ASSERT_OBJECT_SAFE: Option<&(dyn Translate + Sync)> = None;
+
+/// Provides methods for cleaning up unused entries.
+pub trait CleanUp {
+    /// Remove all empty P1-P3 tables
+    ///
+    /// ## Safety
+    ///
+    /// The caller has to guarantee that it's safe to free page table frames:
+    /// All page table frames must only be used once and only in this page table
+    /// (e.g. no reference counted page tables or reusing the same page tables for different virtual addresses ranges in the same page table).
+    unsafe fn clean_up<D>(&mut self, frame_deallocator: &mut D)
+    where
+        D: FrameDeallocator<Size4KiB>;
+
+    /// Remove all empty P1-P3 tables in a certain range
+    /// ```
+    /// # use core::ops::RangeInclusive;
+    /// # use x86_64::{VirtAddr, structures::paging::{
+    /// #    FrameDeallocator, Size4KiB, MappedPageTable, mapper::{RecursivePageTable, CleanUp}, page::{Page, PageRangeInclusive},
+    /// # }};
+    /// # unsafe fn test(page_table: &mut RecursivePageTable, frame_deallocator: &mut impl FrameDeallocator<Size4KiB>) {
+    /// // clean up all page tables in the lower half of the address space
+    /// let lower_half = Page::range_inclusive(
+    ///     Page::containing_address(VirtAddr::new(0)),
+    ///     Page::containing_address(VirtAddr::new(0x0000_7fff_ffff_ffff)),
+    /// );
+    /// page_table.clean_up_addr_range(lower_half, frame_deallocator);
+    /// # }
+    /// ```
+    ///
+    /// ## Safety
+    ///
+    /// The caller has to guarantee that it's safe to free page table frames:
+    /// All page table frames must only be used once and only in this page table
+    /// (e.g. no reference counted page tables or reusing the same page tables for different virtual addresses ranges in the same page table).
+    unsafe fn clean_up_addr_range<D>(
+        &mut self,
+        range: PageRangeInclusive,
+        frame_deallocator: &mut D,
+    ) where
+        D: FrameDeallocator<Size4KiB>;
+}

src/structures/paging/mapper/offset_page_table.rs

@@ -1,7 +1,8 @@
 #![cfg(target_pointer_width = "64")]
 
 use crate::structures::paging::{
-    frame::PhysFrame, mapper::*, page_table::PageTable, Page, PageTableFlags,
+    frame::PhysFrame, mapper::*, page::PageRangeInclusive, page_table::PageTable, FrameDeallocator,
+    Page, PageTableFlags,
 };
 
 /// A Mapper implementation that requires that the complete physically memory is mapped at some
@@ -264,3 +265,24 @@ impl<'a> Translate for OffsetPageTable<'a> {
         self.inner.translate(addr)
     }
 }
+
+impl<'a> CleanUp for OffsetPageTable<'a> {
+    #[inline]
+    unsafe fn clean_up<D>(&mut self, frame_deallocator: &mut D)
+    where
+        D: FrameDeallocator<Size4KiB>,
+    {
+        self.inner.clean_up(frame_deallocator)
+    }
+
+    #[inline]
+    unsafe fn clean_up_addr_range<D>(
+        &mut self,
+        range: PageRangeInclusive,
+        frame_deallocator: &mut D,
+    ) where
+        D: FrameDeallocator<Size4KiB>,
+    {
+        self.inner.clean_up_addr_range(range, frame_deallocator)
+    }
+}

src/structures/paging/mapper/recursive_page_table.rs

@@ -4,12 +4,12 @@ use core::fmt;
 
 use super::*;
 use crate::registers::control::Cr3;
-use crate::structures::paging::PageTableIndex;
+use crate::structures::paging::page_table::PageTableLevel;
 use crate::structures::paging::{
     frame_alloc::FrameAllocator,
-    page::{AddressNotAligned, NotGiantPageSize},
+    page::{AddressNotAligned, NotGiantPageSize, PageRangeInclusive},
     page_table::{FrameError, PageTable, PageTableEntry, PageTableFlags},
-    Page, PageSize, PhysFrame, Size1GiB, Size2MiB, Size4KiB,
+    FrameDeallocator, Page, PageSize, PageTableIndex, PhysFrame, Size1GiB, Size2MiB, Size4KiB,
 };
 use crate::VirtAddr;
 
@@ -829,6 +829,97 @@ impl<'a> Translate for RecursivePageTable<'a> {
     }
 }
 
+impl<'a> CleanUp for RecursivePageTable<'a> {
+    #[inline]
+    unsafe fn clean_up<D>(&mut self, frame_deallocator: &mut D)
+    where
+        D: FrameDeallocator<Size4KiB>,
+    {
+        self.clean_up_addr_range(
+            PageRangeInclusive {
+                start: Page::from_start_address(VirtAddr::new(0)).unwrap(),
+                end: Page::from_start_address(VirtAddr::new(0xffff_ffff_ffff_f000)).unwrap(),
+            },
+            frame_deallocator,
+        )
+    }
+
+    unsafe fn clean_up_addr_range<D>(
+        &mut self,
+        range: PageRangeInclusive,
+        frame_deallocator: &mut D,
+    ) where
+        D: FrameDeallocator<Size4KiB>,
+    {
+        fn clean_up(
+            recursive_index: PageTableIndex,
+            page_table: &mut PageTable,
+            level: PageTableLevel,
+            range: PageRangeInclusive,
+            frame_deallocator: &mut impl FrameDeallocator<Size4KiB>,
+        ) -> bool {
+            if range.is_empty() {
+                return false;
+            }
+
+            let table_addr = range
+                .start
+                .start_address()
+                .align_down(level.table_address_space_alignment());
+
+            let start = range.start.page_table_index(level);
+            let end = range.end.page_table_index(level);
+
+            if let Some(next_level) = level.next_lower_level() {
+                let offset_per_entry = level.entry_address_space_alignment();
+                for (i, entry) in page_table
+                    .iter_mut()
+                    .enumerate()
+                    .take(usize::from(end) + 1)
+                    .skip(usize::from(start))
+                    .filter(|(i, _)| {
+                        !(level == PageTableLevel::Four && *i == recursive_index.into())
+                    })
+                {
+                    if let Ok(frame) = entry.frame() {
+                        let start = table_addr + (offset_per_entry * (i as u64));
+                        let end = start + (offset_per_entry - 1);
+                        let start = Page::<Size4KiB>::containing_address(start);
+                        let start = start.max(range.start);
+                        let end = Page::<Size4KiB>::containing_address(end);
+                        let end = end.min(range.end);
+                        let page_table =
+                            [p1_ptr, p2_ptr, p3_ptr][level as usize - 2](start, recursive_index);
+                        let page_table = unsafe { &mut *page_table };
+                        if clean_up(
+                            recursive_index,
+                            page_table,
+                            next_level,
+                            Page::range_inclusive(start, end),
+                            frame_deallocator,
+                        ) {
+                            entry.set_unused();
+                            unsafe {
+                                frame_deallocator.deallocate_frame(frame);
+                            }
+                        }
+                    }
+                }
+            }
+
+            page_table.iter().all(PageTableEntry::is_unused)
+        }
+
+        clean_up(
+            self.recursive_index,
+            self.level_4_table(),
+            PageTableLevel::Four,
+            range,
+            frame_deallocator,
+        );
+    }
+}
+
 /// The given page table was not suitable to create a `RecursivePageTable`.
 #[derive(Debug)]
 pub enum InvalidPageTable {