From: Jason Gunthorpe <jgg@ziepe.ca>
To: John Hubbard <jhubbard@nvidia.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>,
"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,
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LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 08/23] vfio, mm: fix get_user_pages_remote() and FOLL_LONGTERM
Date: Wed, 13 Nov 2019 09:02:02 -0400 [thread overview]
Message-ID: <20191113130202.GA26068@ziepe.ca> (raw)
In-Reply-To: <20191113042710.3997854-9-jhubbard@nvidia.com>
On Tue, Nov 12, 2019 at 08:26:55PM -0800, John Hubbard 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.
>
> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Jerome Glisse <jglisse@redhat.com>
> Cc: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> drivers/vfio/vfio_iommu_type1.c | 25 ++-----------------------
> mm/gup.c | 27 ++++++++++++++++++++++-----
> 2 files changed, 24 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index d864277ea16f..7301b710c9a4 100644
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -340,7 +340,6 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
> {
> struct page *page[1];
> struct vm_area_struct *vma;
> - struct vm_area_struct *vmas[1];
> unsigned int flags = 0;
> int ret;
>
> @@ -348,33 +347,13 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
> flags |= FOLL_WRITE;
>
> down_read(&mm->mmap_sem);
> - 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);
> - /*
> - * The lifetime of a vaddr_get_pfn() page pin is
> - * userspace-controlled. In the fs-dax case this could
> - * lead to indefinite stalls in filesystem operations.
> - * Disallow attempts to pin fs-dax pages via this
> - * interface.
> - */
> - if (ret > 0 && vma_is_fsdax(vmas[0])) {
> - ret = -EOPNOTSUPP;
> - put_page(page[0]);
> - }
> - }
> - up_read(&mm->mmap_sem);
> -
> + ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM,
> + page, NULL, NULL);
> if (ret == 1) {
> *pfn = page_to_pfn(page[0]);
> return 0;
Mind the return with the lock held this needs some goto unwind
Jason
next prev parent reply other threads:[~2019-11-13 13:02 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-13 4:26 [PATCH v4 00/23] mm/gup: track dma-pinned pages: FOLL_PIN, FOLL_LONGTERM John Hubbard
2019-11-13 4:26 ` [PATCH v4 01/23] mm/gup: pass flags arg to __gup_device_* functions John Hubbard
2019-11-13 10:50 ` Jan Kara
2019-11-13 4:26 ` [PATCH v4 02/23] mm/gup: factor out duplicate code from four routines John Hubbard
2019-11-13 11:15 ` Jan Kara
2019-11-13 23:12 ` John Hubbard
2019-11-13 4:26 ` [PATCH v4 03/23] mm/gup: move try_get_compound_head() to top, fix minor issues John Hubbard
2019-11-13 10:50 ` Jan Kara
2019-11-13 18:38 ` Ira Weiny
2019-11-13 4:26 ` [PATCH v4 04/23] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages John Hubbard
2019-11-13 10:49 ` Jan Kara
2019-11-13 19:09 ` Jerome Glisse
2019-11-13 19:23 ` Dan Williams
2019-11-13 22:00 ` Dan Williams
2019-11-13 22:46 ` John Hubbard
2019-11-13 22:55 ` Dan Williams
2019-11-13 22:56 ` John Hubbard
2019-11-13 23:03 ` Jerome Glisse
2019-11-13 4:26 ` [PATCH v4 05/23] goldish_pipe: rename local pin_user_pages() routine John Hubbard
2019-11-13 4:26 ` [PATCH v4 06/23] IB/umem: use get_user_pages_fast() to pin DMA pages John Hubbard
2019-11-13 4:26 ` [PATCH v4 07/23] media/v4l2-core: set pages dirty upon releasing DMA buffers John Hubbard
2019-11-13 4:26 ` [PATCH v4 08/23] vfio, mm: fix get_user_pages_remote() and FOLL_LONGTERM John Hubbard
2019-11-13 13:02 ` Jason Gunthorpe [this message]
2019-11-13 19:17 ` Ira Weiny
2019-11-13 20:19 ` John Hubbard
2019-11-13 18:47 ` Ira Weiny
2019-11-13 4:26 ` [PATCH v4 09/23] mm/gup: introduce pin_user_pages*() and FOLL_PIN John Hubbard
2019-11-13 10:43 ` Jan Kara
2019-11-13 18:31 ` Ira Weiny
2019-11-13 18:45 ` Dan Williams
2019-11-13 23:22 ` John Hubbard
2019-11-14 6:08 ` John Hubbard
2019-11-13 18:59 ` Ira Weiny
2019-11-13 20:24 ` John Hubbard
2019-11-13 4:26 ` [PATCH v4 10/23] goldish_pipe: convert to pin_user_pages() and put_user_page() John Hubbard
2019-11-13 4:26 ` [PATCH v4 11/23] IB/{core,hw,umem}: set FOLL_PIN, FOLL_LONGTERM via pin_longterm_pages*() John Hubbard
2019-11-13 4:26 ` [PATCH v4 12/23] mm/process_vm_access: set FOLL_PIN via pin_user_pages_remote() John Hubbard
2019-11-13 4:27 ` [PATCH v4 13/23] drm/via: set FOLL_PIN via pin_user_pages_fast() John Hubbard
2019-11-13 4:27 ` [PATCH v4 14/23] fs/io_uring: set FOLL_PIN via pin_user_pages() John Hubbard
2019-11-13 4:27 ` [PATCH v4 15/23] net/xdp: " John Hubbard
2019-11-13 4:27 ` [PATCH v4 16/23] mm/gup: track FOLL_PIN pages John Hubbard
2019-11-13 4:27 ` [PATCH v4 17/23] media/v4l2-core: pin_longterm_pages (FOLL_PIN) and put_user_page() conversion John Hubbard
2019-11-13 4:27 ` [PATCH v4 18/23] vfio, mm: " John Hubbard
2019-11-13 4:27 ` [PATCH v4 19/23] powerpc: book3s64: convert to pin_longterm_pages() and put_user_page() John Hubbard
2019-11-13 4:27 ` [PATCH v4 20/23] mm/gup_benchmark: use proper FOLL_WRITE flags instead of hard-coding "1" John Hubbard
2019-11-13 19:01 ` Ira Weiny
2019-11-13 4:27 ` [PATCH v4 21/23] mm/gup_benchmark: support pin_user_pages() and related calls John Hubbard
2019-11-13 19:03 ` Ira Weiny
2019-11-13 4:27 ` [PATCH v4 22/23] selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN coverage John Hubbard
2019-11-13 19:06 ` Ira Weiny
2019-11-13 4:27 ` [PATCH v4 23/23] mm/gup: remove support for gup(FOLL_LONGTERM) John Hubbard
2019-11-13 19:09 ` Ira Weiny
2019-11-13 23:27 ` John Hubbard
2019-11-13 4:32 ` [PATCH v4 00/23] mm/gup: track dma-pinned pages: FOLL_PIN, FOLL_LONGTERM John Hubbard
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