linux-kernel - Re: [PATCH v1 08/12] mm/rmap: handle device-exclusive entries correctly in try_to_unmap

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <59feb709-dadc-4d19-857e-49320cca3d98@redhat.com>
Date: Thu, 30 Jan 2025 12:08:42 +0100
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, linux-mm@...ck.org,
 nouveau@...ts.freedesktop.org, Andrew Morton <akpm@...ux-foundation.org>,
 Jérôme Glisse <jglisse@...hat.com>,
 Jonathan Corbet <corbet@....net>, Alex Shi <alexs@...nel.org>,
 Yanteng Si <si.yanteng@...ux.dev>, Karol Herbst <kherbst@...hat.com>,
 Lyude Paul <lyude@...hat.com>, Danilo Krummrich <dakr@...nel.org>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
 Pasha Tatashin <pasha.tatashin@...een.com>, Peter Xu <peterx@...hat.com>,
 Alistair Popple <apopple@...dia.com>, Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH v1 08/12] mm/rmap: handle device-exclusive entries
 correctly in try_to_unmap_one()

On 30.01.25 11:10, Simona Vetter wrote:
> On Wed, Jan 29, 2025 at 12:54:06PM +0100, David Hildenbrand wrote:
>> Ever since commit b756a3b5e7ea ("mm: device exclusive memory access")
>> we can return with a device-exclusive entry from page_vma_mapped_walk().
>>
>> try_to_unmap_one() is not prepared for that, so teach it about these
>> non-present nonswap PTEs.
>>
>> Before that, could we also have triggered this case with device-private
>> entries? Unlikely.
> 
> Just quick comment on this, I'm still pondering all the other aspects.
> 
> device-private memory is entirely owned by the driver, the core mm isn't
> supposed to touch these beyond migrating it back to system memory in
> do_swap_page. Plus using rmap when the driver asks for invalidating
> mappings as needed.
> 
> So no lru, thp, migration or anything initiated by core mm should ever
> happen on these device private pages. If it does, it'd be a bug.

I was not 100% sure about HWPoison handling, that's why I added that 
comment. In other regards I agree: reclaim etc. does not apply.

-- 
Cheers,

David / dhildenb