[RFC PATCH v3 0/2] Providing mount in memfd_restricted() syscall

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This patchset builds upon the memfd_restricted() system call that was
discussed in the ‘KVM: mm: fd-based approach for supporting KVM’ patch
series, at

The tree can be found at:

In this patchset, a modification to the memfd_restricted() syscall is
proposed, which allows userspace to provide a mount, on which the
restrictedmem file will be created and returned from the

Allowing userspace to provide a mount allows userspace to control
various memory binding policies via tmpfs mount options, such as
Transparent HugePage memory allocation policy through
‘huge=always/never’ and NUMA memory allocation policy through

Changes since RFCv2:
+ Tightened semantics to accept only fds of the root of a tmpfs mount,
  as Christian suggested
+ Added permissions check on the inode represented by the fd to guard
  against creation of restrictedmem files on read-only tmpfs
  filesystems or mounts
+ Renamed RMFD_TMPFILE to RMFD_USERMNT to better represent providing a
  userspace mount to create a restrictedmem file on
+ Updated selftests for tighter semantics and added selftests to check
  for permissions

Changes since RFCv1:
+ Use fd to represent mount instead of path string, as Kirill
  suggested. I believe using fds makes this syscall interface more
  aligned with the other syscalls like fsopen(), fsconfig(), and
  fsmount() in terms of using and passing around fds
+ Remove unused variable char *orig_shmem_enabled from selftests

+ Sean’s iteration of the ‘KVM: mm: fd-based approach for supporting
  KVM’ patch series at
+ Proposed fixes for these issues mentioned on the mailing list:
    + https://lore.kernel.org/lkml/diqzzga0fv96.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/

Links to earlier patch series:
+ RFC v2: https://lore.kernel.org/lkml/cover.1679428901.git.ackerleytng@xxxxxxxxxx/T/
+ RFC v1: https://lore.kernel.org/lkml/cover.1676507663.git.ackerleytng@xxxxxxxxxx/T/


Ackerley Tng (2):
  mm: restrictedmem: Allow userspace to specify mount for
  selftests: restrictedmem: Check hugepage-ness of shmem file backing
    restrictedmem fd

 include/linux/syscalls.h                      |   2 +-
 include/uapi/linux/restrictedmem.h            |   8 +
 mm/restrictedmem.c                            |  74 ++-
 tools/testing/selftests/Makefile              |   1 +
 .../selftests/restrictedmem/.gitignore        |   3 +
 .../testing/selftests/restrictedmem/Makefile  |  15 +
 .../testing/selftests/restrictedmem/common.c  |   9 +
 .../testing/selftests/restrictedmem/common.h  |   8 +
 .../restrictedmem_hugepage_test.c             | 486 ++++++++++++++++++
 9 files changed, 599 insertions(+), 7 deletions(-)
 create mode 100644 include/uapi/linux/restrictedmem.h
 create mode 100644 tools/testing/selftests/restrictedmem/.gitignore
 create mode 100644 tools/testing/selftests/restrictedmem/Makefile
 create mode 100644 tools/testing/selftests/restrictedmem/common.c
 create mode 100644 tools/testing/selftests/restrictedmem/common.h
 create mode 100644 tools/testing/selftests/restrictedmem/restrictedmem_hugepage_test.c


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