Re: [PATCH v7 01/14] mm: Add F_SEAL_AUTO_ALLOCATE seal to memfd

On 7/21/22 11:44, David Hildenbrand wrote:

Also, I*think* you can place pages via userfaultfd into shmem. Not sure if that would count "auto alloc", but it would certainly bypass fallocate().

Yeah, userfaultfd_register would probably have to forbid this for F_SEAL_AUTO_ALLOCATE vmas. Maybe the memfile_node can be reused for this, adding a new MEMFILE_F_NO_AUTO_ALLOCATE flags? Then userfault_register would do something like memfile_node_get_flags(vma->vm_file) and check the result.

This means moving this patch later, after "mm: Introduce memfile_notifier".

Thanks,

Paolo