Messages in this thread | | | Date | Thu, 23 Feb 2023 00:55:16 +0000 | Subject | Re: [RFC PATCH 1/2] mm: restrictedmem: Allow userspace to specify mount_path for memfd_restricted | From | Ackerley Tng <> |
| |
"Kirill A. Shutemov" <kirill@shutemov.name> writes:
> On Thu, Feb 16, 2023 at 12:41:16AM +0000, Ackerley Tng wrote: >> By default, the backing shmem file for a restrictedmem fd is created >> on shmem's kernel space mount.
>> With this patch, an optional tmpfs mount can be specified, which will >> be used as the mountpoint for backing the shmem file associated with a >> restrictedmem fd.
>> This change is modeled after how sys_open() can create an unnamed >> temporary file in a given directory with O_TMPFILE.
>> This will help restrictedmem fds inherit the properties of the >> provided tmpfs mounts, for example, hugepage allocation hints, NUMA >> binding hints, etc.
>> Signed-off-by: Ackerley Tng <ackerleytng@google.com> >> --- >> include/linux/syscalls.h | 2 +- >> include/uapi/linux/restrictedmem.h | 8 ++++ >> mm/restrictedmem.c | 63 +++++++++++++++++++++++++++--- >> 3 files changed, 66 insertions(+), 7 deletions(-) >> create mode 100644 include/uapi/linux/restrictedmem.h
>> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h >> index f9e9e0c820c5..4b8efe9a8680 100644 >> --- a/include/linux/syscalls.h >> +++ b/include/linux/syscalls.h >> @@ -1056,7 +1056,7 @@ asmlinkage long sys_memfd_secret(unsigned int >> flags); >> asmlinkage long sys_set_mempolicy_home_node(unsigned long start, >> unsigned long len, >> unsigned long home_node, >> unsigned long flags); >> -asmlinkage long sys_memfd_restricted(unsigned int flags); >> +asmlinkage long sys_memfd_restricted(unsigned int flags, const char >> __user *mount_path);
>> /* >> * Architecture-specific system calls
> I'm not sure what the right practice now: do we provide string that > contains mount path or fd that represents the filesystem (returned from > fsmount(2) or open_tree(2)).
> fd seems more flexible: it allows to specify unbind mounts.
I tried out the suggestion of passing fds to memfd_restricted() instead of strings.
One benefit I see of using fds is interface uniformity: it feels more aligned with other syscalls like fsopen(), fsconfig(), and fsmount() in terms of using and passing around fds.
Other than being able to use a mount without a path attached to the mount, are there any other benefits of using fds over using the path string?
Should I post the patches that allows specifying a mount using fds? Should I post them as a separate RFC, or as a new revision to this RFC?
| |