linux-kernel - [PATCH v3 0/6] vfio, dax: prevent long term filesystem-dax pins and other fixes

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Date:   Fri, 23 Feb 2018 16:43:05 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     linux-nvdimm@...ts.01.org
Cc:     Jane Chu <jane.chu@...cle.com>,
        Haozhong Zhang <haozhong.zhang@...el.com>,
        Michal Hocko <mhocko@...e.com>, Jan Kara <jack@...e.cz>,
        kvm@...r.kernel.org, "Darrick J. Wong" <darrick.wong@...cle.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-mm@...ck.org,
        Alex Williamson <alex.williamson@...hat.com>,
        Gerd Rausch <gerd.rausch@...cle.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org,
        kbuild test robot <fengguang.wu@...el.com>,
        Christoph Hellwig <hch@....de>
Subject: [PATCH v3 0/6] vfio,
 dax: prevent long term filesystem-dax pins and other fixes

Changes since v2 [1]:

* Fix yet more 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

---

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.

---

Dan Williams (6):
      dax: fix vma_is_fsdax() helper
      dax: fix dax_mapping() definition in the FS_DAX=n + DEV_DAX=y case
      xfs, dax: introduce IS_FSDAX()
      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 +++++++++++++++---
 fs/xfs/xfs_file.c               |   14 +++++++-------
 fs/xfs/xfs_ioctl.c              |    4 ++--
 fs/xfs/xfs_iomap.c              |    6 +++---
 fs/xfs/xfs_reflink.c            |    2 +-
 include/linux/dax.h             |    9 ++++++---
 include/linux/fs.h              |    8 ++++++--
 7 files changed, 40 insertions(+), 21 deletions(-)