[RFC PATCH v2 0/2] Providing mount in memfd_restricted() syscall

[Ackerley Tng <ackerleytng@google.com>]

Hello,

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
https://lore.kernel.org/lkml/20221202061347.1070246-1-chao.p.peng@linux.intel.com/T/#m7e944d7892afdd1d62a03a287bd488c56e377b0c

The tree can be found at:
https://github.com/googleprodkernel/linux-cc/tree/restrictedmem-provide-mount-fd

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
memfd_restricted().

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
'mpol=local/bind:*'.

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

Dependencies:
+ Sean's iteration of the ‘KVM: mm: fd-based approach for supporting
  KVM’ patch series at
  https://github.com/sean-jc/linux/tree/x86/upm_base_support
+ Proposed fixes for these issues mentioned on the mailing list:
    + https://lore.kernel.org/lkml/diqzzga0fv96.fsf@ackerleytng-cloudtop-sg.c.googlers.com/

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

Ackerley Tng (2):
  mm: restrictedmem: Allow userspace to specify mount for
    memfd_restricted
  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                            |  63 ++-
 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             | 459 ++++++++++++++++++
 9 files changed, 561 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

--
2.40.0.rc2.332.ga46443480c-goog