linux-kernel - Re: [PATCH v2 00/11] Remove device private pages from physical address space

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Message-Id: <20260107120608.5ccd2cc7e4227d2e80028bd9@linux-foundation.org>
Date: Wed, 7 Jan 2026 12:06:08 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Jordan Niethe <jniethe@...dia.com>
Cc: linux-mm@...ck.org, balbirs@...dia.com, matthew.brost@...el.com,
 linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 david@...hat.com, ziy@...dia.com, apopple@...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,
 linuxppc-dev@...ts.ozlabs.org, intel-xe@...ts.freedesktop.org,
 jgg@...pe.ca, Felix.Kuehling@....com
Subject: Re: [PATCH v2 00/11] Remove device private pages from physical
 address space

On Wed,  7 Jan 2026 20:18:12 +1100 Jordan Niethe <jniethe@...dia.com> 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.

Welcome to Linux MM.  That's a heck of an opening salvo ;)

> Needing allocation of physical address space has some problems:
> 
>   1) There may be insufficient physical address space to represent the
>      device memory. KASLR reducing the physical address space and VM
>      configurations with limited physical address space increase the
>      likelihood of hitting this especially as device memory increases. This
>      has been observed to prevent device private from being initialized.  
> 
>   2) Attempting to add the device private pages to the linear map at
>      addresses beyond the actual physical memory causes issues on
>      architectures like aarch64  - meaning the feature does not work there [0].

Can you better help us understand the seriousness of these problems? 
How much are our users really hurting from this?

> Seeking opinions on using the mpfns like this or if a new type would be
> preferred.

Whose opinions?  IOW, can you suggest who you'd like to see review this
work?

> 
> * NOTE: I will need help in testing the driver changes *
> 

Again, please name names ;)  I'm not afraid to prod.


I'm reluctant to add this to mm.git's development/testing branches at
this time.  Your advice on when you think we're ready for that step
would be valuable, thanks.