On Mon, Dec 16, 2024 at 3:51 PM Andreas Hindborg <a.hindborg@xxxxxxxxxx> wrote:
>
> "Alice Ryhl" <aliceryhl@xxxxxxxxxx> writes:
>
> > 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@xxxxxxxxxx> (for mm bits)
> > Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
> > ---
> > rust/kernel/mm/virt.rs | 71 +++++++++++++++++++++++++++++++++++++++++++++++++-
> > 1 file changed, 70 insertions(+), 1 deletion(-)
> >
> > diff --git a/rust/kernel/mm/virt.rs b/rust/kernel/mm/virt.rs
> > index 68c763169cf0..3a23854e14f4 100644
> > --- a/rust/kernel/mm/virt.rs
> > +++ b/rust/kernel/mm/virt.rs
> > @@ -4,7 +4,15 @@
> >
> > //! Virtual memory.
> >
> > -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.
> > ///
> > @@ -100,6 +108,67 @@ pub fn zap_page_range_single(&self, address: usize, size: usize) {
> > )
> > };
> > }
> > +
> > + /// Check whether the `VM_MIXEDMAP` flag is set.
>
> Perhaps "Check whether the `VM_MIXEDMAP` flag is set. If so, return
> `Some`, otherwise `None` ?
How about
If the `VM_MIXEDMAP` flag is set, returns a `VmAreaMixedMap` to this
VMA, otherwise returns `None`.
This follows the example of slice::as_ascii
> > + ///
> > + /// 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.
>
> Could we have a link to `VmAreaRef` and explain that this is a
> `VmAreaRef` with an additional requirement?
Ok.
> > +///
> > +/// # 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.
>
> Maybe something like this: "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."
Ok.
Alice
