linux-kernel - Re: [PATCH v3 0/2] rust: page: Add support for existing struct page mappings

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Message-ID: <CAMwc25pC_jU-bZEBWZB6TQKfFFJs4R+Ero1mA=X=0FBWNFeMXg@mail.gmail.com>
Date: Fri, 22 Nov 2024 16:58:13 +1000
From: David Airlie <airlied@...hat.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: Abdiel Janulgue <abdiel.janulgue@...il.com>, Boqun Feng <boqun.feng@...il.com>, 
	Alice Ryhl <aliceryhl@...gle.com>, rust-for-linux@...r.kernel.org, 
	Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...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>, Danilo Krummrich <dakr@...nel.org>, 
	Wedson Almeida Filho <wedsonaf@...il.com>, Valentin Obst <kernel@...entinobst.de>, 
	open list <linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org>, 
	"open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>, Kairui Song <ryncsn@...il.com>
Subject: Re: [PATCH v3 0/2] rust: page: Add support for existing struct page mappings

On Fri, Nov 22, 2024 at 11:24 AM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Fri, Nov 22, 2024 at 01:18:28AM +0200, Abdiel Janulgue wrote:
> > We need an abstraction of struct page to construct a scatterlist which is
> > needed for an internal firmware structure. Now most of pages needed there
> > come from vmalloc_to_page() which, unlike the current rust Page abstraction,
> > not allocated on demand but is an existing mapping.
> >
> > Hope that clears things up!
>
> That's very helpful!  So the lifetime of the scatterllist must not
> outlive the lifetime of the vmalloc allocation.  That means you can call
> kmap_local_page() on the page in the scatterlist without worrying about
> the refcount of the struct page.  BTW, you can't call page_address() on
> vmalloc memory because vmalloc can allocate pages from HIGHMEM.  Unless
> you're willing to disable support for 32-bit systems with highmem ...
>

https://elixir.bootlin.com/linux/v6.11.5/source/drivers/gpu/drm/nouveau/nvkm/core/firmware.c#L266

This is the C code we want to rustify.

Dave.