6 files changed, 266 insertions, 2 deletions

diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
index 2692cf90c948..84ee7e9d7b0e 100644
--- a/rust/kernel/alloc/allocator.rs
+++ b/rust/kernel/alloc/allocator.rs
@@ -15,8 +15,12 @@ use core::ptr::NonNull;
 
 use crate::alloc::{AllocError, Allocator};
 use crate::bindings;
+use crate::page;
 use crate::pr_warn;
 
+mod iter;
+pub use self::iter::VmallocPageIter;
+
 /// The contiguous kernel allocator.
 ///
 /// `Kmalloc` is typically used for physically contiguous allocations up to page size, but also
@@ -142,6 +146,54 @@ unsafe impl Allocator for Kmalloc {
     }
 }
 
+impl Vmalloc {
+    /// Convert a pointer to a [`Vmalloc`] allocation to a [`page::BorrowedPage`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use core::ptr::{NonNull, from_mut};
+    /// # use kernel::{page, prelude::*};
+    /// use kernel::alloc::allocator::Vmalloc;
+    ///
+    /// let mut vbox = VBox::<[u8; page::PAGE_SIZE]>::new_uninit(GFP_KERNEL)?;
+    ///
+    /// {
+    ///     // SAFETY: By the type invariant of `Box` the inner pointer of `vbox` is non-null.
+    ///     let ptr = unsafe { NonNull::new_unchecked(from_mut(&mut *vbox)) };
+    ///
+    ///     // SAFETY:
+    ///     // `ptr` is a valid pointer to a `Vmalloc` allocation.
+    ///     // `ptr` is valid for the entire lifetime of `page`.
+    ///     let page = unsafe { Vmalloc::to_page(ptr.cast()) };
+    ///
+    ///     // SAFETY: There is no concurrent read or write to the same page.
+    ///     unsafe { page.fill_zero_raw(0, page::PAGE_SIZE)? };
+    /// }
+    /// # Ok::<(), Error>(())
+    /// ```
+    ///
+    /// # Safety
+    ///
+    /// - `ptr` must be a valid pointer to a [`Vmalloc`] allocation.
+    /// - `ptr` must remain valid for the entire duration of `'a`.
+    pub unsafe fn to_page<'a>(ptr: NonNull<u8>) -> page::BorrowedPage<'a> {
+        // SAFETY: `ptr` is a valid pointer to `Vmalloc` memory.
+        let page = unsafe { bindings::vmalloc_to_page(ptr.as_ptr().cast()) };
+
+        // SAFETY: `vmalloc_to_page` returns a valid pointer to a `struct page` for a valid pointer
+        // to `Vmalloc` memory.
+        let page = unsafe { NonNull::new_unchecked(page) };
+
+        // SAFETY:
+        // - `page` is a valid pointer to a `struct page`, given that by the safety requirements of
+        //   this function `ptr` is a valid pointer to a `Vmalloc` allocation.
+        // - By the safety requirements of this function `ptr` is valid for the entire lifetime of
+        //   `'a`.
+        unsafe { page::BorrowedPage::from_raw(page) }
+    }
+}
+
 // SAFETY: `realloc` delegates to `ReallocFunc::call`, which guarantees that
 // - memory remains valid until it is explicitly freed,
 // - passing a pointer to a valid memory allocation is OK,
diff --git a/rust/kernel/alloc/allocator/iter.rs b/rust/kernel/alloc/allocator/iter.rs
new file mode 100644
index 000000000000..5759f86029b7
--- /dev/null
+++ b/rust/kernel/alloc/allocator/iter.rs
@@ -0,0 +1,102 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use super::Vmalloc;
+use crate::page;
+use core::marker::PhantomData;
+use core::ptr::NonNull;
+
+/// An [`Iterator`] of [`page::BorrowedPage`] items owned by a [`Vmalloc`] allocation.
+///
+/// # Guarantees
+///
+/// The pages iterated by the [`Iterator`] appear in the order as they are mapped in the CPU's
+/// virtual address space ascendingly.
+///
+/// # Invariants
+///
+/// - `buf` is a valid and [`page::PAGE_SIZE`] aligned pointer into a [`Vmalloc`] allocation.
+/// - `size` is the number of bytes from `buf` until the end of the [`Vmalloc`] allocation `buf`
+///   points to.
+pub struct VmallocPageIter<'a> {
+    /// The base address of the [`Vmalloc`] buffer.
+    buf: NonNull<u8>,
+    /// The size of the buffer pointed to by `buf` in bytes.
+    size: usize,
+    /// The current page index of the [`Iterator`].
+    index: usize,
+    _p: PhantomData<page::BorrowedPage<'a>>,
+}
+
+impl<'a> Iterator for VmallocPageIter<'a> {
+    type Item = page::BorrowedPage<'a>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let offset = self.index.checked_mul(page::PAGE_SIZE)?;
+
+        // Even though `self.size()` may be smaller than `Self::page_count() * page::PAGE_SIZE`, it
+        // is always a number between `(Self::page_count() - 1) * page::PAGE_SIZE` and
+        // `Self::page_count() * page::PAGE_SIZE`, hence the check below is sufficient.
+        if offset < self.size() {
+            self.index += 1;
+        } else {
+            return None;
+        }
+
+        // TODO: Use `NonNull::add()` instead, once the minimum supported compiler version is
+        // bumped to 1.80 or later.
+        //
+        // SAFETY: `offset` is in the interval `[0, (self.page_count() - 1) * page::PAGE_SIZE]`,
+        // hence the resulting pointer is guaranteed to be within the same allocation.
+        let ptr = unsafe { self.buf.as_ptr().add(offset) };
+
+        // SAFETY: `ptr` is guaranteed to be non-null given that it is derived from `self.buf`.
+        let ptr = unsafe { NonNull::new_unchecked(ptr) };
+
+        // SAFETY:
+        // - `ptr` is a valid pointer to a `Vmalloc` allocation.
+        // - `ptr` is valid for the duration of `'a`.
+        Some(unsafe { Vmalloc::to_page(ptr) })
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let remaining = self.page_count().saturating_sub(self.index);
+
+        (remaining, Some(remaining))
+    }
+}
+
+impl<'a> VmallocPageIter<'a> {
+    /// Creates a new [`VmallocPageIter`] instance.
+    ///
+    /// # Safety
+    ///
+    /// - `buf` must be a [`page::PAGE_SIZE`] aligned pointer into a [`Vmalloc`] allocation.
+    /// - `buf` must be valid for at least the lifetime of `'a`.
+    /// - `size` must be the number of bytes from `buf` until the end of the [`Vmalloc`] allocation
+    ///   `buf` points to.
+    pub unsafe fn new(buf: NonNull<u8>, size: usize) -> Self {
+        // INVARIANT: By the safety requirements, `buf` is a valid and `page::PAGE_SIZE` aligned
+        // pointer into a [`Vmalloc`] allocation.
+        Self {
+            buf,
+            size,
+            index: 0,
+            _p: PhantomData,
+        }
+    }
+
+    /// Returns the size of the backing [`Vmalloc`] allocation in bytes.
+    ///
+    /// Note that this is the size the [`Vmalloc`] allocation has been allocated with. Hence, this
+    /// number may be smaller than `[`Self::page_count`] * [`page::PAGE_SIZE`]`.
+    #[inline]
+    pub fn size(&self) -> usize {
+        self.size
+    }
+
+    /// Returns the number of pages owned by the backing [`Vmalloc`] allocation.
+    #[inline]
+    pub fn page_count(&self) -> usize {
+        self.size().div_ceil(page::PAGE_SIZE)
+    }
+}
diff --git a/rust/kernel/alloc/allocator_test.rs b/rust/kernel/alloc/allocator_test.rs
index 90dd987d40e4..7b10e276f621 100644
--- a/rust/kernel/alloc/allocator_test.rs
+++ b/rust/kernel/alloc/allocator_test.rs
@@ -12,8 +12,10 @@
 use super::{flags::*, AllocError, Allocator, Flags};
 use core::alloc::Layout;
 use core::cmp;
+use core::marker::PhantomData;
 use core::ptr;
 use core::ptr::NonNull;
+use kernel::page;
 
 /// The userspace allocator based on libc.
 pub struct Cmalloc;
@@ -33,6 +35,33 @@ impl Cmalloc {
     }
 }
 
+pub struct VmallocPageIter<'a> {
+    _p: PhantomData<page::BorrowedPage<'a>>,
+}
+
+impl<'a> Iterator for VmallocPageIter<'a> {
+    type Item = page::BorrowedPage<'a>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        None
+    }
+}
+
+impl<'a> VmallocPageIter<'a> {
+    #[allow(clippy::missing_safety_doc)]
+    pub unsafe fn new(_buf: NonNull<u8>, _size: usize) -> Self {
+        Self { _p: PhantomData }
+    }
+
+    pub fn size(&self) -> usize {
+        0
+    }
+
+    pub fn page_count(&self) -> usize {
+        0
+    }
+}
+
 extern "C" {
     #[link_name = "aligned_alloc"]
     fn libc_aligned_alloc(align: usize, size: usize) -> *mut crate::ffi::c_void;
diff --git a/rust/kernel/alloc/kbox.rs b/rust/kernel/alloc/kbox.rs
index 856d05aa60f1..b69ff4a1d748 100644
--- a/rust/kernel/alloc/kbox.rs
+++ b/rust/kernel/alloc/kbox.rs
@@ -3,7 +3,7 @@
 //! Implementation of [`Box`].
 
 #[allow(unused_imports)] // Used in doc comments.
-use super::allocator::{KVmalloc, Kmalloc, Vmalloc};
+use super::allocator::{KVmalloc, Kmalloc, Vmalloc, VmallocPageIter};
 use super::{AllocError, Allocator, Flags};
 use core::alloc::Layout;
 use core::borrow::{Borrow, BorrowMut};
@@ -18,6 +18,7 @@ use core::result::Result;
 
 use crate::ffi::c_void;
 use crate::init::InPlaceInit;
+use crate::page::AsPageIter;
 use crate::types::ForeignOwnable;
 use pin_init::{InPlaceWrite, Init, PinInit, ZeroableOption};
 
@@ -598,3 +599,40 @@ where
         unsafe { A::free(self.0.cast(), layout) };
     }
 }
+
+/// # Examples
+///
+/// ```
+/// # use kernel::prelude::*;
+/// use kernel::alloc::allocator::VmallocPageIter;
+/// use kernel::page::{AsPageIter, PAGE_SIZE};
+///
+/// let mut vbox = VBox::new((), GFP_KERNEL)?;
+///
+/// assert!(vbox.page_iter().next().is_none());
+///
+/// let mut vbox = VBox::<[u8; PAGE_SIZE]>::new_uninit(GFP_KERNEL)?;
+///
+/// let page = vbox.page_iter().next().expect("At least one page should be available.\n");
+///
+/// // SAFETY: There is no concurrent read or write to the same page.
+/// unsafe { page.fill_zero_raw(0, PAGE_SIZE)? };
+/// # Ok::<(), Error>(())
+/// ```
+impl<T> AsPageIter for VBox<T> {
+    type Iter<'a>
+        = VmallocPageIter<'a>
+    where
+        T: 'a;
+
+    fn page_iter(&mut self) -> Self::Iter<'_> {
+        let ptr = self.0.cast();
+        let size = core::mem::size_of::<T>();
+
+        // SAFETY:
+        // - `ptr` is a valid pointer to the beginning of a `Vmalloc` allocation.
+        // - `ptr` is guaranteed to be valid for the lifetime of `'a`.
+        // - `size` is the size of the `Vmalloc` allocation `ptr` points to.
+        unsafe { VmallocPageIter::new(ptr, size) }
+    }
+}
diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs
index 3c72e0bdddb8..ac438e70a1ed 100644
--- a/rust/kernel/alloc/kvec.rs
+++ b/rust/kernel/alloc/kvec.rs
@@ -3,10 +3,11 @@
 //! Implementation of [`Vec`].
 
 use super::{
-    allocator::{KVmalloc, Kmalloc, Vmalloc},
+    allocator::{KVmalloc, Kmalloc, Vmalloc, VmallocPageIter},
     layout::ArrayLayout,
     AllocError, Allocator, Box, Flags,
 };
+use crate::page::AsPageIter;
 use core::{
     borrow::{Borrow, BorrowMut},
     fmt,
@@ -1017,6 +1018,43 @@ where
     }
 }
 
+/// # Examples
+///
+/// ```
+/// # use kernel::prelude::*;
+/// use kernel::alloc::allocator::VmallocPageIter;
+/// use kernel::page::{AsPageIter, PAGE_SIZE};
+///
+/// let mut vec = VVec::<u8>::new();
+///
+/// assert!(vec.page_iter().next().is_none());
+///
+/// vec.reserve(PAGE_SIZE, GFP_KERNEL)?;
+///
+/// let page = vec.page_iter().next().expect("At least one page should be available.\n");
+///
+/// // SAFETY: There is no concurrent read or write to the same page.
+/// unsafe { page.fill_zero_raw(0, PAGE_SIZE)? };
+/// # Ok::<(), Error>(())
+/// ```
+impl<T> AsPageIter for VVec<T> {
+    type Iter<'a>
+        = VmallocPageIter<'a>
+    where
+        T: 'a;
+
+    fn page_iter(&mut self) -> Self::Iter<'_> {
+        let ptr = self.ptr.cast();
+        let size = self.layout.size();
+
+        // SAFETY:
+        // - `ptr` is a valid pointer to the beginning of a `Vmalloc` allocation.
+        // - `ptr` is guaranteed to be valid for the lifetime of `'a`.
+        // - `size` is the size of the `Vmalloc` allocation `ptr` points to.
+        unsafe { VmallocPageIter::new(ptr, size) }
+    }
+}
+
 /// An [`Iterator`] implementation for [`Vec`] that moves elements out of a vector.
 ///
 /// This structure is created by the [`Vec::into_iter`] method on [`Vec`] (provided by the
diff --git a/rust/kernel/alloc/layout.rs b/rust/kernel/alloc/layout.rs
index 93ed514f7cc7..666accb7859c 100644
--- a/rust/kernel/alloc/layout.rs
+++ b/rust/kernel/alloc/layout.rs
@@ -98,6 +98,11 @@ impl<T> ArrayLayout<T> {
     pub const fn is_empty(&self) -> bool {
         self.len == 0
     }
+
+    /// Returns the size of the [`ArrayLayout`] in bytes.
+    pub const fn size(&self) -> usize {
+        self.len() * core::mem::size_of::<T>()
+    }
 }
 
 impl<T> From<ArrayLayout<T>> for Layout {