Re: [PATCH v4 5/9] mm: introduce copy-on-fork VMAs and make VM_MAYBE_GUARD one

["David Hildenbrand (Red Hat)" <david@kernel.org>]

On 18.11.25 11:17, Lorenzo Stoakes wrote:
> Gather all the VMA flags whose presence implies that page tables must be
> copied on fork into a single bitmap - VM_COPY_ON_FORK - and use this
> rather than specifying individual flags in vma_needs_copy().
> 
> We also add VM_MAYBE_GUARD to this list, as it being set on a VMA implies
> that there may be metadata contained in the page tables (that is - guard
> markers) which would will not and cannot be propagated upon fork.
> 
> This was already being done manually previously in vma_needs_copy(), but
> this makes it very explicit, alongside VM_PFNMAP, VM_MIXEDMAP and
> VM_UFFD_WP all of which imply the same.
> 
> Note that VM_STICKY flags ought generally to be marked VM_COPY_ON_FORK too
> - because equally a flag being VM_STICKY indicates that the VMA contains
> metadat that is not propagated by being faulted in - i.e.  that the VMA
> metadata does not fully describe the VMA alone, and thus we must propagate
> whatever metadata there is on a fork.
> 
> However, for maximum flexibility, we do not make this necessarily the case
> here.
> 
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> Reviewed-by: Pedro Falcato <pfalcato@suse.de>
> Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
> ---

Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>

-- 
Cheers

David