From: Jason Gunthorpe <jgg@mellanox.com>
To: "Koenig, Christian" <Christian.Koenig@amd.com>
Cc: "Yang, Philip" <Philip.Yang@amd.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Ralph Campbell <rcampbell@nvidia.com>,
"linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
John Hubbard <jhubbard@nvidia.com>,
"Kuehling, Felix" <Felix.Kuehling@amd.com>,
"amd-gfx@lists.freedesktop.org" <amd-gfx@lists.freedesktop.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
Jerome Glisse <jglisse@redhat.com>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>,
Ben Skeggs <bskeggs@redhat.com>
Subject: Re: [PATCH hmm 00/15] Consolidate the mmu notifier interval_tree and locking
Date: Fri, 18 Oct 2019 20:36:18 +0000 [thread overview]
Message-ID: <20191018203608.GA5670@mellanox.com> (raw)
In-Reply-To: <d6bcbd2a-2519-8945-eaf5-4f4e738c7fa9@amd.com>
On Thu, Oct 17, 2019 at 04:47:20PM +0000, Koenig, Christian wrote:
> > get_user_pages/hmm_range_fault() and invalidate_range_start() both are
> > called while holding mm->map_sem, so they are always serialized.
>
> Not even remotely.
>
> For calling get_user_pages()/hmm_range_fault() you only need to hold the
> mmap_sem in read mode.
Right
> And IIRC invalidate_range_start() is sometimes called without holding
> the mmap_sem at all.
Yep
> So again how are they serialized?
The 'driver lock' thing does it, read the hmm documentation, the hmm
approach is basically the only approach that was correct of all the
drivers..
So long as the 'driver lock' is held the range cannot become
invalidated as the 'driver lock' prevents progress of invalidation.
Holding the driver lock and using the seq based mmu_range_read_retry()
tells if the previous unlocked get_user_pages() is still valid or
needs to be discard.
So it doesn't matter if get_user_pages() races or not, the result is not
to be used until the driver lock is held and mmu_range_read_retry()
called, which provides the coherence.
It is the usual seqlock pattern.
Jason
WARNING: multiple messages have this Message-ID (diff)
From: Jason Gunthorpe <jgg-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
To: "Koenig, Christian" <Christian.Koenig-5C7GfCeVMHo@public.gmane.org>
Cc: Andrea Arcangeli
<aarcange-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
"Yang, Philip" <Philip.Yang-5C7GfCeVMHo@public.gmane.org>,
Ralph Campbell
<rcampbell-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>,
"linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
John Hubbard <jhubbard-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>,
"Kuehling, Felix" <Felix.Kuehling-5C7GfCeVMHo@public.gmane.org>,
"amd-gfx-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org"
<amd-gfx-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org>,
"linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org"
<linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org>,
Jerome Glisse <jglisse-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
"dri-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org"
<dri-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org>,
Ben Skeggs <bskeggs-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH hmm 00/15] Consolidate the mmu notifier interval_tree and locking
Date: Fri, 18 Oct 2019 20:36:18 +0000 [thread overview]
Message-ID: <20191018203608.GA5670@mellanox.com> (raw)
In-Reply-To: <d6bcbd2a-2519-8945-eaf5-4f4e738c7fa9-5C7GfCeVMHo@public.gmane.org>
On Thu, Oct 17, 2019 at 04:47:20PM +0000, Koenig, Christian wrote:
> > get_user_pages/hmm_range_fault() and invalidate_range_start() both are
> > called while holding mm->map_sem, so they are always serialized.
>
> Not even remotely.
>
> For calling get_user_pages()/hmm_range_fault() you only need to hold the
> mmap_sem in read mode.
Right
> And IIRC invalidate_range_start() is sometimes called without holding
> the mmap_sem at all.
Yep
> So again how are they serialized?
The 'driver lock' thing does it, read the hmm documentation, the hmm
approach is basically the only approach that was correct of all the
drivers..
So long as the 'driver lock' is held the range cannot become
invalidated as the 'driver lock' prevents progress of invalidation.
Holding the driver lock and using the seq based mmu_range_read_retry()
tells if the previous unlocked get_user_pages() is still valid or
needs to be discard.
So it doesn't matter if get_user_pages() races or not, the result is not
to be used until the driver lock is held and mmu_range_read_retry()
called, which provides the coherence.
It is the usual seqlock pattern.
Jason
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amd-gfx mailing list
amd-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/amd-gfx
next prev parent reply other threads:[~2019-10-18 20:36 UTC|newest]
Thread overview: 138+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-15 18:12 [PATCH hmm 00/15] Consolidate the mmu notifier interval_tree and locking Jason Gunthorpe
2019-10-15 18:12 ` Jason Gunthorpe
2019-10-15 18:12 ` [PATCH hmm 01/15] mm/mmu_notifier: define the header pre-processor parts even if disabled Jason Gunthorpe
2019-10-15 18:12 ` Jason Gunthorpe
2019-10-21 18:32 ` Jerome Glisse
2019-10-21 18:32 ` Jerome Glisse
2019-10-15 18:12 ` [PATCH hmm 02/15] mm/mmu_notifier: add an interval tree notifier Jason Gunthorpe
2019-10-15 18:12 ` Jason Gunthorpe
2019-10-21 18:30 ` Jerome Glisse
2019-10-21 18:30 ` Jerome Glisse
2019-10-21 18:54 ` Jason Gunthorpe
2019-10-21 18:54 ` Jason Gunthorpe
2019-10-21 19:11 ` Jerome Glisse
2019-10-21 19:11 ` Jerome Glisse
2019-10-21 19:24 ` Jason Gunthorpe
2019-10-21 19:24 ` Jason Gunthorpe
2019-10-21 19:47 ` Jerome Glisse
2019-10-21 19:47 ` Jerome Glisse
2019-10-27 23:15 ` Jason Gunthorpe
2019-10-27 23:15 ` Jason Gunthorpe
2019-10-27 23:15 ` Jason Gunthorpe
2019-10-15 18:12 ` [PATCH hmm 03/15] mm/hmm: allow hmm_range to be used with a mmu_range_notifier or hmm_mirror Jason Gunthorpe
2019-10-15 18:12 ` Jason Gunthorpe
2019-10-21 18:33 ` Jerome Glisse
2019-10-21 18:33 ` Jerome Glisse
2019-10-15 18:12 ` [PATCH hmm 04/15] mm/hmm: define the pre-processor related parts of hmm.h even if disabled Jason Gunthorpe
2019-10-15 18:12 ` Jason Gunthorpe
2019-10-21 18:31 ` Jerome Glisse
2019-10-21 18:31 ` Jerome Glisse
2019-10-15 18:12 ` [PATCH hmm 05/15] RDMA/odp: Use mmu_range_notifier_insert() Jason Gunthorpe
2019-10-15 18:12 ` Jason Gunthorpe
2019-11-04 20:25 ` Jason Gunthorpe
2019-11-04 20:25 ` Jason Gunthorpe
2019-11-04 20:25 ` Jason Gunthorpe
2019-10-15 18:12 ` [PATCH hmm 06/15] RDMA/hfi1: Use mmu_range_notifier_inset for user_exp_rcv Jason Gunthorpe
2019-10-15 18:12 ` Jason Gunthorpe
2019-10-29 12:15 ` Dennis Dalessandro
2019-10-29 12:15 ` Dennis Dalessandro
2019-10-29 12:15 ` Dennis Dalessandro
2019-10-15 18:12 ` [PATCH hmm 07/15] drm/radeon: use mmu_range_notifier_insert Jason Gunthorpe
2019-10-15 18:12 ` Jason Gunthorpe
2019-10-15 18:12 ` [PATCH hmm 08/15] xen/gntdev: Use select for DMA_SHARED_BUFFER Jason Gunthorpe
2019-10-15 18:12 ` [Xen-devel] " Jason Gunthorpe
2019-10-15 18:12 ` Jason Gunthorpe
2019-10-16 5:11 ` Jürgen Groß
2019-10-16 5:11 ` [Xen-devel] " Jürgen Groß
2019-10-16 5:11 ` Jürgen Groß
2019-10-16 6:35 ` Oleksandr Andrushchenko
2019-10-16 6:35 ` [Xen-devel] " Oleksandr Andrushchenko
2019-10-16 6:35 ` Oleksandr Andrushchenko
2019-10-21 19:12 ` Jason Gunthorpe
2019-10-21 19:12 ` [Xen-devel] " Jason Gunthorpe
2019-10-21 19:12 ` Jason Gunthorpe
2019-10-28 6:25 ` [Xen-devel] " Oleksandr Andrushchenko
2019-10-28 6:25 ` Oleksandr Andrushchenko
2019-10-28 6:25 ` Oleksandr Andrushchenko
2019-10-28 6:25 ` Oleksandr Andrushchenko
2019-10-28 6:25 ` Oleksandr Andrushchenko
2019-10-15 18:12 ` [PATCH hmm 09/15] xen/gntdev: use mmu_range_notifier_insert Jason Gunthorpe
2019-10-15 18:12 ` [Xen-devel] " Jason Gunthorpe
2019-10-15 18:12 ` Jason Gunthorpe
2019-10-15 18:12 ` [PATCH hmm 10/15] nouveau: use mmu_notifier directly for invalidate_range_start Jason Gunthorpe
2019-10-15 18:12 ` Jason Gunthorpe
2019-10-15 18:12 ` [PATCH hmm 11/15] nouveau: use mmu_range_notifier instead of hmm_mirror Jason Gunthorpe
2019-10-15 18:12 ` Jason Gunthorpe
2019-10-15 18:12 ` [PATCH hmm 12/15] drm/amdgpu: Call find_vma under mmap_sem Jason Gunthorpe
2019-10-15 18:12 ` Jason Gunthorpe
2019-10-15 18:12 ` [PATCH hmm 13/15] drm/amdgpu: Use mmu_range_insert instead of hmm_mirror Jason Gunthorpe
2019-10-15 18:12 ` Jason Gunthorpe
2019-10-15 18:12 ` [PATCH hmm 14/15] drm/amdgpu: Use mmu_range_notifier " Jason Gunthorpe
2019-10-15 18:12 ` Jason Gunthorpe
2019-10-15 18:12 ` [PATCH hmm 15/15] mm/hmm: remove hmm_mirror and related Jason Gunthorpe
2019-10-15 18:12 ` Jason Gunthorpe
2019-10-21 18:38 ` Jerome Glisse
2019-10-21 18:38 ` Jerome Glisse
2019-10-21 18:57 ` Jason Gunthorpe
2019-10-21 18:57 ` Jason Gunthorpe
2019-10-21 19:19 ` Jerome Glisse
2019-10-21 19:19 ` Jerome Glisse
2019-10-16 8:58 ` [PATCH hmm 00/15] Consolidate the mmu notifier interval_tree and locking Christian König
2019-10-16 8:58 ` Christian König
2019-10-16 16:04 ` Jason Gunthorpe
2019-10-16 16:04 ` Jason Gunthorpe
2019-10-17 8:54 ` Christian König
2019-10-17 8:54 ` Christian König
2019-10-17 16:26 ` Yang, Philip
2019-10-17 16:26 ` Yang, Philip
2019-10-17 16:47 ` Koenig, Christian
2019-10-17 16:47 ` Koenig, Christian
2019-10-18 20:36 ` Jason Gunthorpe [this message]
2019-10-18 20:36 ` Jason Gunthorpe
2019-10-20 14:21 ` Koenig, Christian
2019-10-20 14:21 ` Koenig, Christian
2019-10-21 13:57 ` Jason Gunthorpe
2019-10-21 13:57 ` Jason Gunthorpe
2019-10-21 14:28 ` Koenig, Christian
2019-10-21 14:28 ` Koenig, Christian
2019-10-21 15:12 ` Jason Gunthorpe
2019-10-21 15:12 ` Jason Gunthorpe
2019-10-22 7:57 ` Daniel Vetter
2019-10-22 7:57 ` Daniel Vetter
2019-10-22 15:01 ` Jason Gunthorpe
2019-10-22 15:01 ` Jason Gunthorpe
2019-10-23 9:08 ` Daniel Vetter
2019-10-23 9:08 ` Daniel Vetter
2019-10-23 9:08 ` Daniel Vetter
2019-10-23 9:32 ` Christian König
2019-10-23 9:32 ` Christian König
2019-10-23 9:32 ` Christian König
2019-10-23 16:52 ` Jerome Glisse
2019-10-23 16:52 ` Jerome Glisse
2019-10-23 16:52 ` Jerome Glisse
2019-10-23 16:52 ` Jerome Glisse
2019-10-23 17:24 ` Jason Gunthorpe
2019-10-23 17:24 ` Jason Gunthorpe
2019-10-23 17:24 ` Jason Gunthorpe
2019-10-23 17:24 ` Jason Gunthorpe
2019-10-24 2:16 ` Christoph Hellwig
2019-10-24 2:16 ` Christoph Hellwig
2019-10-24 2:16 ` Christoph Hellwig
2019-10-21 15:55 ` Dennis Dalessandro
2019-10-21 15:55 ` Dennis Dalessandro
2019-10-21 16:58 ` Jason Gunthorpe
2019-10-21 16:58 ` Jason Gunthorpe
2019-10-22 11:56 ` Dennis Dalessandro
2019-10-22 11:56 ` Dennis Dalessandro
2019-10-22 14:37 ` Jason Gunthorpe
2019-10-22 14:37 ` Jason Gunthorpe
2019-10-21 18:40 ` Jerome Glisse
2019-10-21 18:40 ` Jerome Glisse
2019-10-21 19:06 ` Jason Gunthorpe
2019-10-21 19:06 ` Jason Gunthorpe
2019-10-23 20:26 ` Jerome Glisse
2019-10-23 20:26 ` Jerome Glisse
2019-10-23 20:26 ` Jerome Glisse
2019-10-23 20:26 ` Jerome Glisse
2019-10-17 16:44 Koenig, Christian
2019-10-17 16:44 ` Koenig, Christian
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