From: John Hubbard <jhubbard@nvidia•com>
To: Andrew Morton <akpm@linux-foundation•org>
Cc: "Michal Hocko" <mhocko@suse•com>, "Jan Kara" <jack@suse•cz>,
kvm@vger•kernel.org, linux-doc@vger•kernel.org,
"David Airlie" <airlied@linux•ie>,
"Dave Chinner" <david@fromorbit•com>,
dri-devel@lists•freedesktop.org,
LKML <linux-kernel@vger•kernel.org>,
linux-mm@kvack•org, "Paul Mackerras" <paulus@samba•org>,
linux-kselftest@vger•kernel.org,
"Ira Weiny" <ira.weiny@intel•com>,
"Jonathan Corbet" <corbet@lwn•net>,
linux-rdma@vger•kernel.org,
"Christoph Hellwig" <hch@infradead•org>,
"Jason Gunthorpe" <jgg@ziepe•ca>,
"Jason Gunthorpe" <jgg@mellanox•com>,
"Vlastimil Babka" <vbabka@suse•cz>,
"Björn Töpel" <bjorn.topel@intel•com>,
linux-media@vger•kernel.org, "Shuah Khan" <shuah@kernel•org>,
"John Hubbard" <jhubbard@nvidia•com>,
linux-block@vger•kernel.org, "Jérôme Glisse" <jglisse@redhat•com>,
"Al Viro" <viro@zeniv•linux.org.uk>,
"Dan Williams" <dan.j.williams@intel•com>,
"Mauro Carvalho Chehab" <mchehab@kernel•org>,
"Magnus Karlsson" <magnus.karlsson@intel•com>,
"Jens Axboe" <axboe@kernel•dk>,
netdev@vger•kernel.org,
"Alex Williamson" <alex.williamson@redhat•com>,
"Daniel Vetter" <daniel@ffwll•ch>,
linux-fsdevel@vger•kernel.org, bpf@vger•kernel.org,
linuxppc-dev@lists•ozlabs.org,
"David S . Miller" <davem@davemloft•net>,
"Mike Kravetz" <mike.kravetz@oracle•com>
Subject: [PATCH v6 09/24] vfio, mm: fix get_user_pages_remote() and FOLL_LONGTERM
Date: Tue, 19 Nov 2019 00:16:28 -0800 [thread overview]
Message-ID: <20191119081643.1866232-10-jhubbard@nvidia.com> (raw)
In-Reply-To: <20191119081643.1866232-1-jhubbard@nvidia.com>
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(-)
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index d864277ea16f..c7a111ad9975 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ 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 +347,14 @@ 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;
+ ret = 0;
+ goto done;
}
- down_read(&mm->mmap_sem);
-
vaddr = untagged_addr(vaddr);
vma = find_vma_intersection(mm, vaddr, vaddr + 1);
@@ -384,7 +364,7 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
if (is_invalid_reserved_pfn(*pfn))
ret = 0;
}
-
+done:
up_read(&mm->mmap_sem);
return ret;
}
diff --git a/mm/gup.c b/mm/gup.c
index 14fcdc502166..cce2c9676853 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -29,6 +29,13 @@ struct follow_page_context {
unsigned int page_mask;
};
+static __always_inline long __gup_longterm_locked(struct task_struct *tsk,
+ struct mm_struct *mm,
+ unsigned long start,
+ unsigned long nr_pages,
+ struct page **pages,
+ struct vm_area_struct **vmas,
+ unsigned int flags);
/*
* Return the compound head page with ref appropriately incremented,
* or NULL if that failed.
@@ -1167,13 +1174,23 @@ long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
struct vm_area_struct **vmas, int *locked)
{
/*
- * FIXME: Current FOLL_LONGTERM behavior is incompatible with
+ * Parts of FOLL_LONGTERM behavior are incompatible with
* FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on
- * vmas. As there are no users of this flag in this call we simply
- * disallow this option for now.
+ * vmas. However, this only comes up if locked is set, and there are
+ * callers that do request FOLL_LONGTERM, but do not set locked. So,
+ * allow what we can.
*/
- if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
- return -EINVAL;
+ if (gup_flags & FOLL_LONGTERM) {
+ if (WARN_ON_ONCE(locked))
+ return -EINVAL;
+ /*
+ * This will check the vmas (even if our vmas arg is NULL)
+ * and return -ENOTSUPP if DAX isn't allowed in this case:
+ */
+ return __gup_longterm_locked(tsk, mm, start, nr_pages, pages,
+ vmas, gup_flags | FOLL_TOUCH |
+ FOLL_REMOTE);
+ }
return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
locked,
--
2.24.0
next prev parent reply other threads:[~2019-11-19 8:40 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-19 8:16 [PATCH v6 00/24] mm/gup: track dma-pinned pages: FOLL_PIN John Hubbard
2019-11-19 8:16 ` [PATCH v6 01/24] mm/gup: pass flags arg to __gup_device_* functions John Hubbard
2019-11-19 8:16 ` [PATCH v6 02/24] mm/gup: factor out duplicate code from four routines John Hubbard
2019-11-19 10:19 ` Jan Kara
2019-11-19 8:16 ` [PATCH v6 03/24] mm/gup: move try_get_compound_head() to top, fix minor issues John Hubbard
2019-11-19 8:16 ` [PATCH v6 04/24] mm: Cleanup __put_devmap_managed_page() vs ->page_free() John Hubbard
2019-11-19 8:16 ` [PATCH v6 05/24] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages John Hubbard
2019-11-19 8:16 ` [PATCH v6 06/24] goldish_pipe: rename local pin_user_pages() routine John Hubbard
2019-11-19 8:16 ` [PATCH v6 07/24] IB/umem: use get_user_pages_fast() to pin DMA pages John Hubbard
2019-11-19 8:16 ` [PATCH v6 08/24] media/v4l2-core: set pages dirty upon releasing DMA buffers John Hubbard
2019-11-19 8:16 ` John Hubbard [this message]
2019-11-19 8:16 ` [PATCH v6 10/24] mm/gup: introduce pin_user_pages*() and FOLL_PIN John Hubbard
2019-11-19 8:16 ` [PATCH v6 11/24] goldish_pipe: convert to pin_user_pages() and put_user_page() John Hubbard
2019-11-19 8:16 ` [PATCH v6 12/24] IB/{core, hw, umem}: set FOLL_PIN via pin_user_pages*(), fix up ODP John Hubbard
2019-11-19 8:16 ` [PATCH v6 13/24] mm/process_vm_access: set FOLL_PIN via pin_user_pages_remote() John Hubbard
2019-11-19 8:16 ` [PATCH v6 14/24] drm/via: set FOLL_PIN via pin_user_pages_fast() John Hubbard
2019-11-19 8:16 ` [PATCH v6 15/24] fs/io_uring: set FOLL_PIN via pin_user_pages() John Hubbard
2019-11-19 16:10 ` Jens Axboe
2019-11-20 7:03 ` John Hubbard
2019-11-19 8:16 ` [PATCH v6 16/24] net/xdp: " John Hubbard
2019-11-19 8:16 ` [PATCH v6 17/24] mm/gup: track FOLL_PIN pages John Hubbard
2019-11-19 11:37 ` Jan Kara
2019-11-20 7:17 ` John Hubbard
2019-11-19 8:16 ` [PATCH v6 18/24] media/v4l2-core: pin_user_pages (FOLL_PIN) and put_user_page() conversion John Hubbard
2019-11-19 8:16 ` [PATCH v6 19/24] vfio, mm: " John Hubbard
2019-11-19 8:16 ` [PATCH v6 20/24] powerpc: book3s64: convert to pin_user_pages() and put_user_page() John Hubbard
2019-11-19 8:16 ` [PATCH v6 21/24] mm/gup_benchmark: use proper FOLL_WRITE flags instead of hard-coding "1" John Hubbard
2019-11-19 8:16 ` [PATCH v6 22/24] mm/gup_benchmark: support pin_user_pages() and related calls John Hubbard
2019-11-19 8:16 ` [PATCH v6 23/24] selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN coverage John Hubbard
2019-11-19 8:16 ` [PATCH v6 24/24] mm, tree-wide: rename put_user_page*() to unpin_user_page*() John Hubbard
2019-11-19 11:39 ` Jan Kara
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