Re: [PATCH v17 10/10] rust: page: add `from_raw()`

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] The `Page::from_raw` method silently bypasses the documented type invariants of the `Page` struct and lacks an `// INVARIANT:` comment.
--

commit 224010a6541ae8f534f1577d76a1acd3e9bb5d34
Author: Andreas Hindborg <a.hindborg@kernel.org>

rust: page: add `from_raw()`

This commit adds a new from_raw() method to the Page struct. It enables the
creation of a shared &Page reference directly from a raw struct page C
pointer.

> diff --git a/rust/kernel/page.rs b/rust/kernel/page.rs
> index 844c75e541345..d56ae597f6926 100644
> --- a/rust/kernel/page.rs
> +++ b/rust/kernel/page.rs

[ ... ]

> @@ -214,6 +214,18 @@ pub fn nid(&self) -> i32 {
>          unsafe { bindings::page_to_nid(self.as_ptr()) }
>      }
>  
> +    /// Create a `&Page` from a raw `struct page` pointer.
> +    ///
> +    /// # Safety
> +    ///
> +    /// `ptr` must be convertible to a shared reference with a lifetime of `'a`.
> +    #[inline]
> +    pub unsafe fn from_raw<'a>(ptr: *const bindings::page) -> &'a Self {
> +        // SAFETY: By function safety requirements, `ptr` is not null and is convertible to a shared
> +        // reference.
> +        unsafe { &*ptr.cast() }

[Severity: Low]
This isn't a bug, but should this unsafe block include an `// INVARIANT:`
comment to justify the type invariants of the Page struct?

The Page struct has an `# Invariants` documentation section stating that it
has ownership over the page. While that ownership invariant might be an
obsolete leftover, creating a &Page reference here conceptually asserts that
the referenced memory satisfies this type invariant.

Could we add the required `// INVARIANT:` comment or update the outdated
type invariant documentation to clarify this?

> +    }
> +
>      /// Runs a piece of code with this page mapped to an address.
>      ///
>      /// The page is unmapped when this call returns.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260604-unique-ref-v17-0-7b4c3d2930b9@kernel.org?part=10