linux-kernel - Re: [RFC PATCH 0/6] Remove device private pages from physical address space

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Message-ID: <dklhe7gbudew5mdgrxzhrw3wqnnqigapbtetnn4gpaktlkpiyh@kohwt6syeapn>
Date: Mon, 1 Dec 2025 10:33:20 +1100
From: Alistair Popple <apopple@...dia.com>
To: "David Hildenbrand (Red Hat)" <david@...nel.org>
Cc: Jordan Niethe <jniethe@...dia.com>, linux-mm@...ck.org, 
	balbirs@...dia.com, matthew.brost@...el.com, akpm@...ux-foundation.org, 
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org, ziy@...dia.com, 
	lorenzo.stoakes@...cle.com, lyude@...hat.com, dakr@...nel.org, airlied@...il.com, 
	simona@...ll.ch, rcampbell@...dia.com, mpenttil@...hat.com, jgg@...dia.com, 
	willy@...radead.org
Subject: Re: [RFC PATCH 0/6] Remove device private pages from physical
 address space

On 2025-11-28 at 18:40 +1100, "David Hildenbrand (Red Hat)" <david@...nel.org> wrote...
> On 11/28/25 05:41, Jordan Niethe wrote:
> > Today, when creating these device private struct pages, the first step
> > is to use request_free_mem_region() to get a range of physical address
> > space large enough to represent the devices memory. This allocated
> > physical address range is then remapped as device private memory using
> > memremap_pages.
> 
> Just a note that as we are finishing the old release and are about to start
> the merge window (+ there is Thanksgiving), expect few replies to non-urgent
> stuff in the next weeks.

Thanks David! Mostly we just wanted to at least get the RFC out prior to LPC so
I can talk about it there if needed.

> Having that said, the proposal is interesting. I recall that Alistair and
> Jason recently discussed removing the need of dealing with PFNs
> completely for device-private.
> 
> Is that the result of these discussions?

That is certainly something we would like to explore, but this idea mostly came
from a more immediate need to deal with the lack of support on AARCH64 where we
can't just steal random bits of the physical address space (which is reasonable
- the kernel doesn't really "own" the physical memory map after all), and also
the KASLR and VM issues which cause initialisation to fail.

Removing struct pages entirely for at least device private memory is also
something I'd like to explore with this.

> -- 
> Cheers
> 
> David