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From: Jason Gunthorpe <jgg@nvidia.com>
To: Peter Xu <peterx@redhat.com>
Cc: Alistair Popple <apopple@nvidia.com>,
	linux-mm@kvack.org, nouveau@lists.freedesktop.org,
	bskeggs@redhat.com, akpm@linux-foundation.org,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	dri-devel@lists.freedesktop.org, jhubbard@nvidia.com,
	rcampbell@nvidia.com, jglisse@redhat.com, hch@infradead.org,
	daniel@ffwll.ch, willy@infradead.org, bsingharora@gmail.com,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v8 5/8] mm: Device exclusive memory access
Date: Tue, 18 May 2021 14:33:34 -0300	[thread overview]
Message-ID: <20210518173334.GE1002214@nvidia.com> (raw)
In-Reply-To: <YKP5Dj4Q/riGGc43@t490s>

On Tue, May 18, 2021 at 01:27:42PM -0400, Peter Xu wrote:

> I also have a pure and high level question regarding a process fork() when
> there're device exclusive ptes: would the two processes then own the device
> together?  Is this a real usecase?

If the pages are MAP_SHARED then yes. All VMAs should point at the
same device_exclusive page and all VMA should migrate back to CPU
pages together.

> Indeed it'll be odd for a COW page since for COW page then it means after
> parent/child writting to the page it'll clone into two, then it's a mistery on
> which one will be the one that "exclusived owned" by the device..

For COW pages it is like every other fork case.. We can't reliably
write-protect the device_exclusive page during fork so we must copy it
at fork time.

Thus three reasonable choices:
 - Copy to a new CPU page
 - Migrate back to a CPU page and write protect it
 - Copy to a new device exclusive page

Jason

  reply	other threads:[~2021-05-18 17:33 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-07  8:42 [PATCH v8 0/8] Add support for SVM atomics in Nouveau Alistair Popple
2021-04-07  8:42 ` [PATCH v8 1/8] mm: Remove special swap entry functions Alistair Popple
2021-05-18  2:17   ` Peter Xu
2021-05-18 11:58     ` Alistair Popple
2021-05-18 14:17       ` Peter Xu
2021-04-07  8:42 ` [PATCH v8 2/8] mm/swapops: Rework swap entry manipulation code Alistair Popple
2021-04-07  8:42 ` [PATCH v8 3/8] mm/rmap: Split try_to_munlock from try_to_unmap Alistair Popple
2021-05-18 20:04   ` Liam Howlett
2021-05-19 12:38     ` Alistair Popple
2021-05-20 20:24       ` Liam Howlett
2021-05-21  2:23         ` Alistair Popple
2021-04-07  8:42 ` [PATCH v8 4/8] mm/rmap: Split migration into its own function Alistair Popple
2021-04-07  8:42 ` [PATCH v8 5/8] mm: Device exclusive memory access Alistair Popple
2021-05-18  2:08   ` Peter Xu
2021-05-18 13:19     ` Alistair Popple
2021-05-18 17:27       ` Peter Xu
2021-05-18 17:33         ` Jason Gunthorpe [this message]
2021-05-18 18:01           ` Peter Xu
2021-05-18 19:45             ` Jason Gunthorpe
2021-05-18 20:29               ` Peter Xu
2021-05-18 23:03                 ` Jason Gunthorpe
2021-05-18 23:45                   ` Peter Xu
2021-05-19 11:04                     ` Alistair Popple
2021-05-19 12:15                       ` Peter Xu
2021-05-19 13:11                         ` Alistair Popple
2021-05-19 14:04                           ` Peter Xu
2021-05-19 13:28                     ` Jason Gunthorpe
2021-05-19 14:09                       ` Peter Xu
2021-05-19 18:11                         ` Jason Gunthorpe
2021-05-19 11:35         ` Alistair Popple
2021-05-19 12:21           ` Peter Xu
2021-05-19 12:46             ` Alistair Popple
2021-05-21  6:53       ` Alistair Popple
2021-05-18 21:16   ` Peter Xu
2021-05-19 10:49     ` Alistair Popple
2021-05-19 12:24       ` Peter Xu
2021-05-19 12:46         ` Alistair Popple
2021-04-07  8:42 ` [PATCH v8 6/8] mm: Selftests for exclusive device memory Alistair Popple
2021-04-07  8:42 ` [PATCH v8 7/8] nouveau/svm: Refactor nouveau_range_fault Alistair Popple
2021-04-07  8:42 ` [PATCH v8 8/8] nouveau/svm: Implement atomic SVM access Alistair Popple
2021-05-21  4:04   ` Ben Skeggs
2021-05-06  7:43 ` [PATCH v8 0/8] Add support for SVM atomics in Nouveau Alistair Popple

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