On 02/22/18 23:17 -0800, Dan Williams wrote: > 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(-) Tested on QEMU with fs-dax and device-dax as vNVDIMM backends respectively with vfio passthrough. The fs-dax case fails QEMU as expected, and the device-dax case works normally now. Tested-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>