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Subject: Re: [PATCH v7 01/14] mm: Add F_SEAL_AUTO_ALLOCATE seal to memfd
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To:     David Hildenbrand <david@redhat.com>,
        Chao Peng <chao.p.peng@linux.intel.com>, kvm@vger.kernel.org,
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From:   Paolo Bonzini <pbonzini@redhat.com>
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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