[PATCH v2 0/5] vfio, dax: prevent long term filesystem-dax pins and other fixes

[Dan Williams]

Changes since v1 [1]:

* Fix the detection of device-dax file instances in vma_is_fsdax().
  (Haozhong, Gerd)

* Fix compile breakage in the FS_DAX=n and DEV_DAX=y case. (0day robot)

[1]: https://lists.01.org/pipermail/linux-nvdimm/2018-February/014046.html

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The vfio interface, like RDMA, wants to setup long term (indefinite)
pins of the pages backing an address range so that a guest or userspace
driver can perform DMA to the with physical address. Given that this
pinning may lead to filesystem operations deadlocking in the
filesystem-dax case, the pinning request needs to be rejected.

The longer term fix for vfio, RDMA, and any other long term pin user, is
to provide a 'pin with lease' mechanism. Similar to the leases that are
hold for pNFS RDMA layouts, this userspace lease gives the kernel a way
to notify userspace that the block layout of the file is changing and
the kernel is revoking access to pinned pages.

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Dan Williams (5):
      dax: fix vma_is_fsdax() helper
      dax: fix dax_mapping() definition in the FS_DAX=n + DEV_DAX=y case
      dax: fix S_DAX definition
      dax: short circuit vma_is_fsdax() in the CONFIG_FS_DAX=n case
      vfio: disable filesystem-dax page pinning


 drivers/vfio/vfio_iommu_type1.c |   18 +++++++++++++++---
 include/linux/dax.h             |    9 ++++++---
 include/linux/fs.h              |    6 ++++--
 3 files changed, 25 insertions(+), 8 deletions(-)