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

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Date:   Thu, 22 Feb 2018 23:17:40 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     linux-nvdimm@...ts.01.org
Cc:     Haozhong Zhang <haozhong.zhang@...el.com>,
        Michal Hocko <mhocko@...e.com>, Jan Kara <jack@...e.cz>,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...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 v2 0/5] vfio,
 dax: prevent long term filesystem-dax pins and other fixes

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

---

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 (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(-)