[PATCH 11/46] mm/huge_memory: properly handle refcounted PUD mappings on fork

[sashiko-bot at kernel.org]

> copy_huge_pud() copies device-DAX entries without taking a folio reference
> or updating mapcounts and the child's RSS.
> 
> For example, MADV_GUARD_INSTALL sets VM_MAYBE_GUARD on a device-DAX VMA,
> forcing copy_page_range() to traverse the whole VMA on fork. Any remaining
> huge PUDs are then copied without accounting for the new mappings.
> Unmapping them in the child decrements accounting that was never added.
> 
> Use vm_normal_page_pud() to identify refcounted mappings. Take a folio
> reference and add the child's PUD rmap and RSS accounting before installing
> the copied entry. Pass src and dst VMAs consistently instead of src and
> dst MM. Move the TODO.
> 
> Fixes: aed877c2b4257 ("device/dax: properly refcount device dax pages when mapping")
> Cc: stable at vger.kernel.org
> Signed-off-by: David Hildenbrand (Arm) <david at kernel.org>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org?part=11