[PATCH v12 3/8] mm: rust: add vm_insert_page

Alice Ryhl
2025-01-15T13:36:12Z

The vm_insert_page method is only usable on vmas with the VM_MIXEDMAP
flag, so we introduce a new type to keep track of such vmas.

The approach used in this patch assumes that we will not need to encode
many flag combinations in the type. I don't think we need to encode more
than VM_MIXEDMAP and VM_PFNMAP as things are now. However, if that
becomes necessary, using generic parameters in a single type would scale
better as the number of flags increases.

Acked-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> (for mm bits)
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
rust/kernel/mm/virt.rs | 79 +++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 78 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/mm/virt.rs b/rust/kernel/mm/virt.rs
index 2c7de0460e0a..ab89a526d3e4 100644
--- a/rust/kernel/mm/virt.rs
+++ b/rust/kernel/mm/virt.rs
@@ -14,7 +14,15 @@
//! ensures that you can't, for example, accidentally call a function that requires holding the
//! write lock when you only hold the read lock.

-use crate::{bindings, mm::MmWithUser, types::Opaque};
+use crate::{
+ bindings,
+ error::{to_result, Result},
+ mm::MmWithUser,
+ page::Page,
+ types::Opaque,
+};
+
+use core::ops::Deref;

/// A wrapper for the kernel's `struct vm_area_struct` with read access.
///
@@ -124,6 +132,75 @@ pub fn zap_page_range_single(&self, address: usize, size: usize) {
)
};
}
+
+ /// If the [`VM_MIXEDMAP`] flag is set, returns a [`VmAreaMixedMap`] to this VMA, otherwise
+ /// returns `None`.
+ ///
+ /// This can be used to access methods that require [`VM_MIXEDMAP`] to be set.
+ ///
+ /// [`VM_MIXEDMAP`]: flags::MIXEDMAP
+ #[inline]
+ pub fn as_mixedmap_vma(&self) -> Option<&VmAreaMixedMap> {
+ if self.flags() & flags::MIXEDMAP != 0 {
+ // SAFETY: We just checked that `VM_MIXEDMAP` is set. All other requirements are
+ // satisfied by the type invariants of `VmAreaRef`.
+ Some(unsafe { VmAreaMixedMap::from_raw(self.as_ptr()) })
+ } else {
+ None
+ }
+ }
+}
+
+/// A wrapper for the kernel's `struct vm_area_struct` with read access and [`VM_MIXEDMAP`] set.
+///
+/// It represents an area of virtual memory.
+///
+/// This struct is identical to [`VmAreaRef`] except that it must only be used when the
+/// [`VM_MIXEDMAP`] flag is set on the vma.
+///
+/// # Invariants
+///
+/// The caller must hold the mmap read lock or the vma read lock. The `VM_MIXEDMAP` flag must be
+/// set.
+///
+/// [`VM_MIXEDMAP`]: flags::MIXEDMAP
+#[repr(transparent)]
+pub struct VmAreaMixedMap {
+ vma: VmAreaRef,
+}
+
+// Make all `VmAreaRef` methods available on `VmAreaMixedMap`.
+impl Deref for VmAreaMixedMap {
+ type Target = VmAreaRef;
+
+ #[inline]
+ fn deref(&self) -> &VmAreaRef {
+ &self.vma
+ }
+}
+
+impl VmAreaMixedMap {
+ /// Access a virtual memory area given a raw pointer.
+ ///
+ /// # Safety
+ ///
+ /// Callers must ensure that `vma` is valid for the duration of 'a, and that the mmap read lock
+ /// (or stronger) is held for at least the duration of 'a. The `VM_MIXEDMAP` flag must be set.
+ #[inline]
+ pub unsafe fn from_raw<'a>(vma: *const bindings::vm_area_struct) -> &'a Self {
+ // SAFETY: The caller ensures that the invariants are satisfied for the duration of 'a.
+ unsafe { &*vma.cast() }
+ }
+
+ /// Maps a single page at the given address within the virtual memory area.
+ ///
+ /// This operation does not take ownership of the page.
+ #[inline]
+ pub fn vm_insert_page(&self, address: usize, page: &Page) -> Result {
+ // SAFETY: By the type invariant of `Self` caller has read access and has verified that
+ // `VM_MIXEDMAP` is set. By invariant on `Page` the page has order 0.
+ to_result(unsafe { bindings::vm_insert_page(self.as_ptr(), address as _, page.as_ptr()) })
+ }
}

/// The integer type used for vma flags.

--
2.48.0.rc2.279.g1de40edade-goog