linux-kernel - Re: [PATCH v10 2/8] mm: rust: add vm_area_struct methods that require read access

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Message-ID: <CAH5fLgjxmpcLJwj5k85O39R00+vRRixA6i3xeK1STe_LQLHkTA@mail.gmail.com>
Date: Thu, 5 Dec 2024 11:40:03 +0100
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>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v10 2/8] mm: rust: add vm_area_struct methods that require
 read access

On Fri, Nov 29, 2024 at 5:32 PM Alice Ryhl <aliceryhl@...gle.com> wrote:
>
> This adds a type called VmAreaRef which is used when referencing a vma
> that you have read access to. Here, read access means that you hold
> either the mmap read lock or the vma read lock (or stronger).
>
> Additionally, a vma_lookup method is added to the mmap read guard, which
> enables you to obtain a &VmAreaRef in safe Rust code.
>
> This patch only provides a way to lock the mmap read lock, but a
> follow-up patch also provides a way to just lock the vma read lock.
>
> Acked-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com> (for mm bits)
> Reviewed-by: Jann Horn <jannh@...gle.com>
> Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>

It looks like binder needs a way to check whether a given vma is
associated with a given mm. I guess we can do that by adding a method
to VmAreaRef that returns a &MmWithUser.

This indicates that vma->vm_mm references an mm with non-zero mm_users
whenever it's legal to have a reference to the vma.

Alice