From: Dan Williams <dan.j.williams@intel.com>
To: linux-nvdimm@lists.01.org
Cc: Haozhong Zhang <haozhong.zhang@intel.com>,
Michal Hocko <mhocko@suse.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
stable@vger.kernel.org, linux-mm@kvack.org,
Alex Williamson <alex.williamson@redhat.com>,
linux-fsdevel@vger.kernel.org, Christoph Hellwig <hch@lst.de>
Subject: [PATCH v4 12/12] vfio: disable filesystem-dax page pinning
Date: Mon, 26 Feb 2018 20:20:58 -0800 [thread overview]
Message-ID: <151970525871.26729.7716403687659267945.stgit@dwillia2-desk3.amr.corp.intel.com> (raw)
In-Reply-To: <151970519370.26729.1011551137381425076.stgit@dwillia2-desk3.amr.corp.intel.com>
Filesystem-DAX is incompatible with 'longterm' page pinning. Without
page cache indirection a DAX mapping maps filesystem blocks directly.
This means that the filesystem must not modify a file's block map while
any page in a mapping is pinned. In order to prevent the situation of
userspace holding of filesystem operations indefinitely, disallow
'longterm' Filesystem-DAX mappings.
RDMA has the same conflict and the plan there is to add a 'with lease'
mechanism to allow the kernel to notify userspace that the mapping is
being torn down for block-map maintenance. Perhaps something similar can
be put in place for vfio.
Note that xfs and ext4 still report:
"DAX enabled. Warning: EXPERIMENTAL, use at your own risk"
...at mount time, and resolving the dax-dma-vs-truncate problem is one
of the last hurdles to remove that designation.
Acked-by: Alex Williamson <alex.williamson@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: kvm@vger.kernel.org
Cc: <stable@vger.kernel.org>
Reported-by: Haozhong Zhang <haozhong.zhang@intel.com>
Fixes: d475c6346a38 ("dax,ext2: replace XIP read and write with DAX I/O")
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
drivers/vfio/vfio_iommu_type1.c | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index e30e29ae4819..45657e2b1ff7 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -338,11 +338,12 @@ 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];
int ret;
if (mm == current->mm) {
- ret = get_user_pages_fast(vaddr, 1, !!(prot & IOMMU_WRITE),
- page);
+ ret = get_user_pages_longterm(vaddr, 1, !!(prot & IOMMU_WRITE),
+ page, vmas);
} else {
unsigned int flags = 0;
@@ -351,7 +352,18 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
down_read(&mm->mmap_sem);
ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags, page,
- NULL, NULL);
+ 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);
}
next prev parent reply other threads:[~2018-02-27 4:30 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-27 4:19 [PATCH v4 00/12] vfio, dax: prevent long term filesystem-dax pins and other fixes Dan Williams
2018-02-27 4:20 ` [PATCH v4 01/12] dax: fix vma_is_fsdax() helper Dan Williams
2018-02-27 4:20 ` [PATCH v4 02/12] dax: introduce IS_DEVDAX() and IS_FSDAX() Dan Williams
2018-02-27 16:54 ` Jan Kara
2018-02-27 4:20 ` [PATCH v4 03/12] ext2, dax: finish implementing dax_sem helpers Dan Williams
2018-02-27 17:00 ` Jan Kara
2018-02-27 4:20 ` [PATCH v4 04/12] ext2, dax: define ext2_dax_*() infrastructure in all cases Dan Williams
2018-02-27 17:01 ` Jan Kara
2018-02-27 4:20 ` [PATCH v4 05/12] ext4, dax: define ext4_dax_*() " Dan Williams
2018-02-27 17:01 ` Jan Kara
2018-02-27 4:20 ` [PATCH v4 06/12] ext2, dax: replace IS_DAX() with IS_FSDAX() Dan Williams
2018-02-27 17:02 ` Jan Kara
2018-02-27 4:20 ` [PATCH v4 07/12] ext4, " Dan Williams
2018-02-27 17:02 ` Jan Kara
2018-02-27 4:20 ` [PATCH v4 08/12] xfs, " Dan Williams
2018-02-27 17:03 ` Jan Kara
2018-02-27 4:20 ` [PATCH v4 09/12] mm, dax: replace IS_DAX() with IS_DEVDAX() or IS_FSDAX() Dan Williams
2018-02-27 17:05 ` Jan Kara
2018-02-27 4:20 ` [PATCH v4 10/12] fs, dax: kill IS_DAX() Dan Williams
2018-02-27 17:06 ` Jan Kara
2018-02-27 4:20 ` [PATCH v4 11/12] dax: fix S_DAX definition Dan Williams
2018-02-27 4:20 ` Dan Williams [this message]
2018-02-27 22:23 ` [PATCH v4 00/12] vfio, dax: prevent long term filesystem-dax pins and other fixes Dave Chinner
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