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

Chao Peng
2022-08-10T09:44:01Z

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