On Fri, Aug 05, 2022 at 07:55:38PM +0200, Paolo Bonzini wrote:
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.
Then we need change userfault_register uAPI for a new property flag. Userspace should still the decision-maker for this flag.
This means moving this patch later, after "mm: Introduce memfile_notifier".
Yes, it makes sense now.
Chao
Thanks,
Paolo