Re: [PATCH v20 4/8] rust: page: convert to `Ownable`'

[Gary Guo]

On Tue Aug 25, 2026 at 2:20 PM BST, Alice Ryhl wrote:
> On Mon, Aug 24, 2026 at 01:17:56PM +0200, Andreas Hindborg wrote:
>> +        // SAFETY: We just successfully allocated a page, so we now have ownership of the newly
>> +        // allocated page. We transfer that ownership to the new `Owned<Page>` object.
>> +        // Since `Page` is transparent, we can cast the pointer directly.
>> +        Ok(unsafe { Owned::from_raw(page.cast()) })
>
> This doesn't satisfy the safety requirements of Owned::from_raw()
> because the page may be used with vm_insert_page(), which increments its
> refcount and causes it to be shared the vma system, and this occurs
> before Page::release() is called.

I suppose the existing vm_insert_page() abstraction we have is already
problematic, because it uses `&Page`?

Maybe we want to change the API to use `ARef<Page>` so it already has to be
shared? Conceptually it takes a reference count from a `&Page`, which isn't
possible because `Page` is not `AlwaysRefCounted`, so it needs a `&ARef<Page>`
to be able to do that op.

Best,
Gary