linux-kernel - Re: [PATCH v1 2/4] mm/mmu_notifier: drop owner from MMU_NOTIFY

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Message-ID: <Z5t-sFymrz5kFafV@phenom.ffwll.local>
Date: Thu, 30 Jan 2025 14:29:20 +0100
From: Simona Vetter <simona.vetter@...ll.ch>
To: David Hildenbrand <david@...hat.com>
Cc: Alistair Popple <apopple@...dia.com>, 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>, Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH v1 2/4] mm/mmu_notifier: drop owner from
 MMU_NOTIFY_EXCLUSIVE

On Thu, Jan 30, 2025 at 10:28:00AM +0100, David Hildenbrand wrote:
> On 30.01.25 06:34, Alistair Popple wrote:
> > Looking at hmm_test I see that doesn't use the sequence counter to ensure
> > the PTE remains valid whilst it is mapped. I think that is probably wrong, so
> > apologies if that lead you astray.
> 
> Yes, the hmm_test does not completely follow the same model the nouveau
> implementation does; so it might not be completely correct.

But unrelated but just crossed my mind:

I guess another crucial difference is that the hw (probably, not sure)
will restart the fault if we don't repair it to its liking. So the
hmm-test does need some kind of retry loop too somewhere to match that.
But might be good to also still land some of the other improvements
discussed in these threads to make make_device_exclusive a bit more
reliable instead of relying on busy-looping throug the hw fault handler
for everything.
-Sima
-- 
Simona Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch