From: John Hubbard <jhubbard@nvidia.com>
To: Jason Gunthorpe <jgg@ziepe.ca>, Jerome Glisse <jglisse@redhat.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"Al Viro" <viro@zeniv.linux.org.uk>,
"Alex Williamson" <alex.williamson@redhat.com>,
"Benjamin Herrenschmidt" <benh@kernel.crashing.org>,
"Björn Töpel" <bjorn.topel@intel.com>,
"Christoph Hellwig" <hch@infradead.org>,
"Dan Williams" <dan.j.williams@intel.com>,
"Daniel Vetter" <daniel@ffwll.ch>,
"Dave Chinner" <david@fromorbit.com>,
"David Airlie" <airlied@linux.ie>,
"David S . Miller" <davem@davemloft.net>,
"Ira Weiny" <ira.weiny@intel.com>, "Jan Kara" <jack@suse.cz>,
"Jens Axboe" <axboe@kernel.dk>,
"Jonathan Corbet" <corbet@lwn.net>,
"Magnus Karlsson" <magnus.karlsson@intel.com>,
"Mauro Carvalho Chehab" <mchehab@kernel.org>,
"Michael Ellerman" <mpe@ellerman.id.au>,
"Michal Hocko" <mhocko@suse.com>,
"Mike Kravetz" <mike.kravetz@oracle.com>,
"Paul Mackerras" <paulus@samba.org>,
"Shuah Khan" <shuah@kernel.org>,
"Vlastimil Babka" <vbabka@suse.cz>,
bpf@vger.kernel.org, dri-devel@lists.freedesktop.org,
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LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 05/18] mm/gup: introduce pin_user_pages*() and FOLL_PIN
Date: Mon, 4 Nov 2019 12:57:59 -0800 [thread overview]
Message-ID: <d0890a8b-c349-0515-2570-10e83979836b@nvidia.com> (raw)
In-Reply-To: <20191104203702.GG30938@ziepe.ca>
On 11/4/19 12:37 PM, Jason Gunthorpe wrote:
> On Mon, Nov 04, 2019 at 03:31:53PM -0500, Jerome Glisse wrote:
>>> Note for Jason: the (a) or (b) items are talking about the vfio case, which is
>>> one of the two call sites that now use pin_longterm_pages_remote(), and the
>>> other one is infiniband:
>>>
>>> drivers/infiniband/core/umem_odp.c:646: npages = pin_longterm_pages_remote(owning_process, owning_mm,
>>> drivers/vfio/vfio_iommu_type1.c:353: ret = pin_longterm_pages_remote(NULL, mm, vaddr, 1,
>>
>> vfio should be reverted until it can be properly implemented.
>> The issue is that when you fix the implementation you might
>> break vfio existing user and thus regress the kernel from user
>> point of view. So i rather have the change to vfio reverted,
>> i believe it was not well understood when it got upstream,
>> between in my 5.4 tree it is still gup_remote not longterm.
>
> It is clearly a bug, vfio must use LONGTERM, and does right above this
> remote call:
>
> if (mm == current->mm) {
> ret = get_user_pages(vaddr, 1, flags | FOLL_LONGTERM, page,
> vmas);
> } else {
> ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags, page,
> vmas, NULL);
>
>
> I'm not even sure that it really makes any sense to build a 'if' like
> that, surely just always call remote??
>
Right, and I thought about this when converting, and realized that the above
code is working around the current gup.c limitations, which are "cannot support
gup remote with FOLL_LONGTERM".
Given that observation, the code is getting itself some FOLL_LONGTERM support
for the non-remote case, and only hitting the limitation if the mm really is
non-current.
And if you look at my patch, it keeps the same behavior, while adding in the
new wrapper calls.
So...thoughts, preferences?
thanks,
John Hubbard
NVIDIA
next prev parent reply other threads:[~2019-11-04 20:58 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-03 21:17 [PATCH v2 00/18] mm/gup: track dma-pinned pages: FOLL_PIN, FOLL_LONGTERM John Hubbard
2019-11-03 21:17 ` [PATCH v2 01/18] mm/gup: pass flags arg to __gup_device_* functions John Hubbard
2019-11-04 16:39 ` Jerome Glisse
2019-11-03 21:17 ` [PATCH v2 02/18] mm/gup: factor out duplicate code from four routines John Hubbard
2019-11-04 16:51 ` Jerome Glisse
2019-11-03 21:17 ` [PATCH v2 03/18] goldish_pipe: rename local pin_user_pages() routine John Hubbard
2019-11-04 16:52 ` Jerome Glisse
2019-11-03 21:17 ` [PATCH v2 04/18] media/v4l2-core: set pages dirty upon releasing DMA buffers John Hubbard
2019-11-10 10:10 ` Hans Verkuil
2019-11-11 21:46 ` John Hubbard
2019-11-03 21:18 ` [PATCH v2 05/18] mm/gup: introduce pin_user_pages*() and FOLL_PIN John Hubbard
2019-11-04 17:33 ` Jerome Glisse
2019-11-04 19:04 ` John Hubbard
2019-11-04 19:18 ` Jerome Glisse
2019-11-04 19:30 ` John Hubbard
2019-11-04 19:52 ` Jerome Glisse
2019-11-04 20:09 ` John Hubbard
2019-11-04 20:31 ` Jason Gunthorpe
2019-11-04 20:40 ` John Hubbard
2019-11-04 20:31 ` Jerome Glisse
2019-11-04 20:37 ` Jason Gunthorpe
2019-11-04 20:57 ` John Hubbard [this message]
2019-11-04 21:15 ` Jason Gunthorpe
2019-11-04 21:34 ` John Hubbard
2019-11-04 20:33 ` David Rientjes
2019-11-04 20:48 ` Jerome Glisse
2019-11-05 13:10 ` Mike Rapoport
2019-11-05 19:00 ` John Hubbard
2019-11-07 2:25 ` Ira Weiny
2019-11-07 8:07 ` Mike Rapoport
2019-11-03 21:18 ` [PATCH v2 06/18] goldish_pipe: convert to pin_user_pages() and put_user_page() John Hubbard
2019-11-03 21:18 ` [PATCH v2 07/18] infiniband: set FOLL_PIN, FOLL_LONGTERM via pin_longterm_pages*() John Hubbard
2019-11-04 20:33 ` Jason Gunthorpe
2019-11-04 20:48 ` John Hubbard
2019-11-04 20:57 ` Jason Gunthorpe
2019-11-04 22:03 ` John Hubbard
2019-11-05 2:32 ` Jason Gunthorpe
2019-11-07 2:26 ` Ira Weiny
2019-11-03 21:18 ` [PATCH v2 08/18] mm/process_vm_access: set FOLL_PIN via pin_user_pages_remote() John Hubbard
2019-11-04 17:41 ` Jerome Glisse
2019-11-03 21:18 ` [PATCH v2 09/18] drm/via: set FOLL_PIN via pin_user_pages_fast() John Hubbard
2019-11-04 17:44 ` Jerome Glisse
2019-11-04 18:22 ` John Hubbard
2019-11-03 21:18 ` [PATCH v2 10/18] fs/io_uring: set FOLL_PIN via pin_user_pages() John Hubbard
2019-11-03 21:18 ` [PATCH v2 11/18] net/xdp: " John Hubbard
2019-11-03 21:18 ` [PATCH v2 12/18] mm/gup: track FOLL_PIN pages John Hubbard
2019-11-04 18:52 ` Jerome Glisse
2019-11-04 22:49 ` John Hubbard
2019-11-04 23:49 ` Jerome Glisse
2019-11-05 0:18 ` John Hubbard
2019-11-03 21:18 ` [PATCH v2 13/18] media/v4l2-core: pin_longterm_pages (FOLL_PIN) and put_user_page() conversion John Hubbard
2019-11-10 10:11 ` Hans Verkuil
2019-11-03 21:18 ` [PATCH v2 14/18] vfio, mm: " John Hubbard
2019-11-03 21:18 ` [PATCH v2 15/18] powerpc: book3s64: convert to pin_longterm_pages() and put_user_page() John Hubbard
2019-11-03 21:18 ` [PATCH v2 16/18] mm/gup_benchmark: support pin_user_pages() and related calls John Hubbard
2019-11-03 21:18 ` [PATCH v2 17/18] selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN coverage John Hubbard
2019-11-03 21:18 ` [PATCH v2 18/18] mm/gup: remove support for gup(FOLL_LONGTERM) John Hubbard
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