From: Andrew Morton <akpm@linux-foundation.org>
To: Alistair Popple <apopple@nvidia.com>
Cc: <linux-mm@kvack.org>, <nouveau@lists.freedesktop.org>,
<bskeggs@redhat.com>, <rcampbell@nvidia.com>,
<linux-doc@vger.kernel.org>, <jhubbard@nvidia.com>,
<bsingharora@gmail.com>, <linux-kernel@vger.kernel.org>,
<dri-devel@lists.freedesktop.org>, <hch@infradead.org>,
<jglisse@redhat.com>, <willy@infradead.org>, <jgg@nvidia.com>,
<peterx@redhat.com>, <hughd@google.com>,
Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v9 07/10] mm: Device exclusive memory access
Date: Mon, 24 May 2021 15:11:57 -0700 [thread overview]
Message-ID: <20210524151157.2dc5d2bb510ff86dc449bf0c@linux-foundation.org> (raw)
In-Reply-To: <20210524132725.12697-8-apopple@nvidia.com>
On Mon, 24 May 2021 23:27:22 +1000 Alistair Popple <apopple@nvidia.com> wrote:
> Some devices require exclusive write access to shared virtual
> memory (SVM) ranges to perform atomic operations on that memory. This
> requires CPU page tables to be updated to deny access whilst atomic
> operations are occurring.
>
> In order to do this introduce a new swap entry
> type (SWP_DEVICE_EXCLUSIVE). When a SVM range needs to be marked for
> exclusive access by a device all page table mappings for the particular
> range are replaced with device exclusive swap entries. This causes any
> CPU access to the page to result in a fault.
>
> Faults are resovled by replacing the faulting entry with the original
> mapping. This results in MMU notifiers being called which a driver uses
> to update access permissions such as revoking atomic access. After
> notifiers have been called the device will no longer have exclusive
> access to the region.
>
> Walking of the page tables to find the target pages is handled by
> get_user_pages() rather than a direct page table walk. A direct page
> table walk similar to what migrate_vma_collect()/unmap() does could also
> have been utilised. However this resulted in more code similar in
> functionality to what get_user_pages() provides as page faulting is
> required to make the PTEs present and to break COW.
>
> ...
>
> Documentation/vm/hmm.rst | 17 ++++
> include/linux/mmu_notifier.h | 6 ++
> include/linux/rmap.h | 4 +
> include/linux/swap.h | 7 +-
> include/linux/swapops.h | 44 ++++++++-
> mm/hmm.c | 5 +
> mm/memory.c | 128 +++++++++++++++++++++++-
> mm/mprotect.c | 8 ++
> mm/page_vma_mapped.c | 9 +-
> mm/rmap.c | 186 +++++++++++++++++++++++++++++++++++
> 10 files changed, 405 insertions(+), 9 deletions(-)
>
This is quite a lot of code added to core MM for a single driver.
Is there any expectation that other drivers will use this code?
Is there a way of reducing the impact (code size, at least) for systems
which don't need this code?
How beneficial is this code to nouveau users? I see that it permits a
part of OpenCL to be implemented, but how useful/important is this in
the real world?
Thanks.
next prev parent reply other threads:[~2021-05-24 22:12 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-24 13:27 [PATCH v9 00/10] Add support for SVM atomics in Nouveau Alistair Popple
2021-05-24 13:27 ` [PATCH v9 01/10] mm: Remove special swap entry functions Alistair Popple
2021-05-24 13:27 ` [PATCH v9 02/10] mm/swapops: Rework swap entry manipulation code Alistair Popple
2021-05-24 13:27 ` [PATCH v9 03/10] mm/rmap: Split try_to_munlock from try_to_unmap Alistair Popple
2021-05-25 18:39 ` Liam Howlett
2021-05-25 23:45 ` Shakeel Butt
2021-06-04 20:49 ` Liam Howlett
2021-06-05 0:41 ` Shakeel Butt
2021-06-05 3:39 ` Liam Howlett
2021-06-05 4:19 ` Shakeel Butt
2021-06-07 4:51 ` Alistair Popple
2021-05-24 13:27 ` [PATCH v9 04/10] mm/rmap: Split migration into its own function Alistair Popple
2021-05-24 13:27 ` [PATCH v9 05/10] mm: Rename migrate_pgmap_owner Alistair Popple
2021-05-26 19:41 ` Peter Xu
2021-05-24 13:27 ` [PATCH v9 06/10] mm/memory.c: Allow different return codes for copy_nonpresent_pte() Alistair Popple
2021-05-26 19:50 ` Peter Xu
2021-05-27 1:20 ` Alistair Popple
2021-05-27 1:44 ` Peter Xu
2021-05-24 13:27 ` [PATCH v9 07/10] mm: Device exclusive memory access Alistair Popple
2021-05-24 22:11 ` Andrew Morton [this message]
2021-05-25 1:31 ` John Hubbard
2021-05-25 9:21 ` Alistair Popple
2021-05-25 11:51 ` Balbir Singh
2021-05-26 7:17 ` John Hubbard
2021-05-26 13:30 ` Alistair Popple
2021-06-02 8:50 ` Balbir Singh
2021-06-02 14:37 ` Peter Xu
2021-06-03 11:39 ` Alistair Popple
2021-06-03 14:47 ` Peter Xu
2021-06-04 1:07 ` Alistair Popple
2021-06-04 15:20 ` Peter Xu
2021-06-03 8:37 ` John Hubbard
2021-05-26 19:28 ` Peter Xu
2021-05-27 3:35 ` Alistair Popple
2021-05-27 13:04 ` Peter Xu
2021-05-28 1:48 ` Alistair Popple
2021-05-28 13:11 ` Peter Xu
2021-05-24 13:27 ` [PATCH v9 08/10] mm: Selftests for exclusive device memory Alistair Popple
2021-05-24 13:27 ` [PATCH v9 09/10] nouveau/svm: Refactor nouveau_range_fault Alistair Popple
2021-05-24 13:27 ` [PATCH v9 10/10] nouveau/svm: Implement atomic SVM access Alistair Popple
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