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From: John Hubbard <jhubbard@nvidia.com>
To: Alex Williamson <alex.williamson@redhat.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"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>,
	"Jason Gunthorpe" <jgg@ziepe.ca>, "Jens Axboe" <axboe@kernel.dk>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"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,
	kvm@vger.kernel.org, linux-block@vger.kernel.org,
	linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-kselftest@vger.kernel.org, linux-media@vger.kernel.org,
	linux-rdma@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	netdev@vger.kernel.org, linux-mm@kvack.org,
	LKML <linux-kernel@vger.kernel.org>,
	"Jason Gunthorpe" <jgg@mellanox.com>
Subject: Re: [PATCH v7 09/24] vfio, mm: fix get_user_pages_remote() and FOLL_LONGTERM
Date: Thu, 21 Nov 2019 13:49:40 -0800
Message-ID: <b5ae788a-58a9-de93-f65e-e4d9c0632dc9@nvidia.com> (raw)
In-Reply-To: <20191121143525.50deb72f@x1.home>

On 11/21/19 1:35 PM, Alex Williamson wrote:
> On Wed, 20 Nov 2019 23:13:39 -0800
> John Hubbard <jhubbard@nvidia.com> wrote:
> 
>> As it says in the updated comment in gup.c: current FOLL_LONGTERM
>> behavior is incompatible with FAULT_FLAG_ALLOW_RETRY because of the
>> FS DAX check requirement on vmas.
>>
>> However, the corresponding restriction in get_user_pages_remote() was
>> slightly stricter than is actually required: it forbade all
>> FOLL_LONGTERM callers, but we can actually allow FOLL_LONGTERM callers
>> that do not set the "locked" arg.
>>
>> Update the code and comments accordingly, and update the VFIO caller
>> to take advantage of this, fixing a bug as a result: the VFIO caller
>> is logically a FOLL_LONGTERM user.
>>
>> Also, remove an unnessary pair of calls that were releasing and
>> reacquiring the mmap_sem. There is no need to avoid holding mmap_sem
>> just in order to call page_to_pfn().
>>
>> Also, move the DAX check ("if a VMA is DAX, don't allow long term
>> pinning") from the VFIO call site, all the way into the internals
>> of get_user_pages_remote() and __gup_longterm_locked(). That is:
>> get_user_pages_remote() calls __gup_longterm_locked(), which in turn
>> calls check_dax_vmas(). It's lightly explained in the comments as well.
>>
>> Thanks to Jason Gunthorpe for pointing out a clean way to fix this,
>> and to Dan Williams for helping clarify the DAX refactoring.
>>
>> Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
>> Reviewed-by: Ira Weiny <ira.weiny@intel.com>
>> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
>> Cc: Dan Williams <dan.j.williams@intel.com>
>> Cc: Jerome Glisse <jglisse@redhat.com>
>> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
>> ---
>>   drivers/vfio/vfio_iommu_type1.c | 30 +++++-------------------------
>>   mm/gup.c                        | 27 ++++++++++++++++++++++-----
>>   2 files changed, 27 insertions(+), 30 deletions(-)
> 
> Tested with device assignment and Intel mdev vGPU assignment with QEMU
> userspace:
> 
> Tested-by: Alex Williamson <alex.williamson@redhat.com>
> Acked-by: Alex Williamson <alex.williamson@redhat.com>
> 
> Feel free to include for 19/24 as well.  Thanks,
> 
> Alex


Great! Thanks for the testing and ack on those. I'm about to repackage
(and split up as CH requested) for 5.5, and will keep you on CC, of course.

thanks,
-- 
John Hubbard
NVIDIA

  reply index

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-21  7:13 [PATCH v7 00/24] mm/gup: track dma-pinned pages: FOLL_PIN John Hubbard
2019-11-21  7:13 ` [PATCH v7 01/24] mm/gup: pass flags arg to __gup_device_* functions John Hubbard
2019-11-21  8:06   ` Christoph Hellwig
2019-11-21  8:25     ` John Hubbard
2019-11-21  7:13 ` [PATCH v7 02/24] mm/gup: factor out duplicate code from four routines John Hubbard
2019-11-21  8:03   ` Christoph Hellwig
2019-11-21  8:29     ` John Hubbard
2019-11-21  9:49       ` Jan Kara
2019-11-21 21:47         ` John Hubbard
2019-11-21  9:54       ` Jan Kara
2019-11-22  2:54         ` John Hubbard
2019-11-22 11:15           ` Jan Kara
2019-11-21  7:13 ` [PATCH v7 03/24] mm/gup: move try_get_compound_head() to top, fix minor issues John Hubbard
2019-11-21  8:07   ` Christoph Hellwig
2019-11-21  7:13 ` [PATCH v7 04/24] mm: Cleanup __put_devmap_managed_page() vs ->page_free() John Hubbard
2019-11-21  8:04   ` Christoph Hellwig
2019-11-21  7:13 ` [PATCH v7 05/24] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages John Hubbard
2019-11-21  8:05   ` Christoph Hellwig
2019-11-21  8:54     ` John Hubbard
2019-11-21 16:59       ` Dan Williams
2019-11-21 22:22         ` John Hubbard
2019-11-21  7:13 ` [PATCH v7 06/24] goldish_pipe: rename local pin_user_pages() routine John Hubbard
2019-11-21  8:08   ` Christoph Hellwig
2019-11-21  8:36     ` John Hubbard
2019-11-21  7:13 ` [PATCH v7 07/24] IB/umem: use get_user_pages_fast() to pin DMA pages John Hubbard
2019-11-21  8:07   ` Christoph Hellwig
2019-11-21 14:36     ` Jason Gunthorpe
2019-11-24  6:14       ` John Hubbard
2019-11-24 10:07       ` Leon Romanovsky
2019-11-25  0:05         ` John Hubbard
2019-11-25  0:53           ` Jason Gunthorpe
2019-11-21  7:13 ` [PATCH v7 08/24] media/v4l2-core: set pages dirty upon releasing DMA buffers John Hubbard
2019-11-21  8:09   ` Christoph Hellwig
2019-11-21  7:13 ` [PATCH v7 09/24] vfio, mm: fix get_user_pages_remote() and FOLL_LONGTERM John Hubbard
2019-11-21  8:10   ` Christoph Hellwig
2019-11-21  8:48     ` John Hubbard
2019-11-21 21:35   ` Alex Williamson
2019-11-21 21:49     ` John Hubbard [this message]
2019-11-21  7:13 ` [PATCH v7 10/24] mm/gup: introduce pin_user_pages*() and FOLL_PIN John Hubbard
2019-11-21  7:13 ` [PATCH v7 11/24] goldish_pipe: convert to pin_user_pages() and put_user_page() John Hubbard
2019-11-21  7:13 ` [PATCH v7 12/24] IB/{core,hw,umem}: set FOLL_PIN via pin_user_pages*(), fix up ODP John Hubbard
2019-11-21  7:13 ` [PATCH v7 13/24] mm/process_vm_access: set FOLL_PIN via pin_user_pages_remote() John Hubbard
2019-11-21  7:13 ` [PATCH v7 14/24] drm/via: set FOLL_PIN via pin_user_pages_fast() John Hubbard
2019-11-21  7:13 ` [PATCH v7 15/24] fs/io_uring: set FOLL_PIN via pin_user_pages() John Hubbard
2019-11-21  7:13 ` [PATCH v7 16/24] net/xdp: " John Hubbard
2019-11-21  7:13 ` [PATCH v7 17/24] mm/gup: track FOLL_PIN pages John Hubbard
2019-11-21  9:39   ` Jan Kara
2019-11-30 18:59   ` kbuild test robot
2019-11-21  7:13 ` [PATCH v7 18/24] media/v4l2-core: pin_user_pages (FOLL_PIN) and put_user_page() conversion John Hubbard
2019-11-21  7:13 ` [PATCH v7 19/24] vfio, mm: " John Hubbard
2019-11-21  7:13 ` [PATCH v7 20/24] powerpc: book3s64: convert to pin_user_pages() and put_user_page() John Hubbard
2019-11-21  7:13 ` [PATCH v7 21/24] mm/gup_benchmark: use proper FOLL_WRITE flags instead of hard-coding "1" John Hubbard
2019-11-21  7:13 ` [PATCH v7 22/24] mm/gup_benchmark: support pin_user_pages() and related calls John Hubbard
2019-11-21  7:13 ` [PATCH v7 23/24] selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN coverage John Hubbard
2019-11-21  7:13 ` [PATCH v7 24/24] mm, tree-wide: rename put_user_page*() to unpin_user_page*() John Hubbard

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