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SubjectRe: [PATCH v5 0/5] MAP_DIRECT and block-map-atomic files
On Wed, Aug 16, 2017 at 12:44 AM, Dan Williams <> wrote:
> Changes since v4 [1]:
> * Drop the new vma ->fs_flags field, it can be replaced by just checking
> ->vm_ops locally in the filesystem. This approach also allows
> non-MAP_DIRECT vmas to be vma_merge() capable since vmas with
> vm_ops->close() disable vma merging. (Jan)
> * Drop the new ->fmmap() operation, instead convert all ->mmap()
> implementations tree-wide to take an extra 'map_flags' parameter.
> (Jan)
> * Drop the cute (MAP_SHARED|MAP_PRIVATE) hack/mechanism to add new
> validated flags mmap(2) and instead just define a new mmap syscall
> variant (sys_mmap_pgoff_strict). (Andy)
> * Fix the fact that MAP_PRIVATE|MAP_DIRECT would silently fallback to
> MAP_SHARED (addressed by the new syscall). (Kirill)
> * Require CAP_LINUX_IMMUTABLE for MAP_DIRECT to close any unforeseen
> denial of service for unmanaged + unprivileged MAP_DIRECT usage.
> (Kirill)
> * Switch MAP_DIRECT fault failures to SIGBUS (Kirill)
> * Add an fcntl mechanism to allow an unprivileged process to use
> MAP_DIRECT on an fd setup by a privileged process.
> * Rework the MAP_DIRECT description to allow for future hardware where
> it may not be required to software-pin the file offset to physical
> address relationship.
> Given the tree-wide touches in this revision the patchset is starting to
> feel more like -mm material than strictly xfs.
> [1]:

For easier testing / evaluation of these patches I went ahead and
rebased them to v4.13-rc5, fixed up 0-day reports from the ->mmap()
conversion, and published a for-4.14/map-direct branch here:

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