linux-kernel - [PATCH v9 3/8] mm: rust: add vm_insert

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Message-ID: <20241122-vma-v9-3-7127bfcdd54e@google.com>
Date: Fri, 22 Nov 2024 15:40:28 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Miguel Ojeda <ojeda@...nel.org>, Matthew Wilcox <willy@...radead.org>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Vlastimil Babka <vbabka@...e.cz>, 
	John Hubbard <jhubbard@...dia.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Arnd Bergmann <arnd@...db.de>, Christian Brauner <brauner@...nel.org>, Jann Horn <jannh@...gle.com>, 
	Suren Baghdasaryan <surenb@...gle.com>
Cc: Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, 
	"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Benno Lossin <benno.lossin@...ton.me>, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	rust-for-linux@...r.kernel.org, Alice Ryhl <aliceryhl@...gle.com>, 
	Andreas Hindborg <a.hindborg@...nel.org>
Subject: [PATCH v9 3/8] mm: rust: add vm_insert_page

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@...cle.com> (for mm bits)
Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
---
 rust/kernel/mm/virt.rs | 70 +++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 69 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/mm/virt.rs b/rust/kernel/mm/virt.rs
index 6df145fea128..3e494e40b530 100644
--- a/rust/kernel/mm/virt.rs
+++ b/rust/kernel/mm/virt.rs
@@ -4,7 +4,14 @@
 
 //! Virtual memory.
 
-use crate::{bindings, types::Opaque};
+use crate::{
+    bindings,
+    error::{to_result, Result},
+    page::Page,
+    types::Opaque,
+};
+
+use core::ops::Deref;
 
 /// A wrapper for the kernel's `struct vm_area_struct` with read access.
 ///
@@ -85,6 +92,67 @@ pub fn zap_page_range_single(&self, address: usize, size: usize) {
             )
         };
     }
+
+    /// Check whether the `VM_MIXEDMAP` flag is set.
+    ///
+    /// This can be used to access methods that require `VM_MIXEDMAP` to be set.
+    #[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.
+///
+/// # Invariants
+///
+/// The caller must hold the mmap read lock or the vma read lock. The `VM_MIXEDMAP` flag must be
+/// set.
+#[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: The caller has read access and has verified that `VM_MIXEDMAP` is set. The page
+        // is order 0. The address is checked on the C side so it can take any value.
+        to_result(unsafe { bindings::vm_insert_page(self.as_ptr(), address as _, page.as_ptr()) })
+    }
 }
 
 /// The integer type used for vma flags.

-- 
2.47.0.371.ga323438b13-goog