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 <redacted>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Reviewed-by: Vlastimil Babka <redacted>
---

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

-- 
Cheers

David