Re: [PATCH v3 3/9] mm/huge_memory: honor MM_CP_TRY_CHANGE_WRITABLE in change_huge_pud()

[sashiko-bot@kernel.org]

> change_protection() applies vma->vm_page_prot, which lacks the write bit
> for CoW and write-notified mappings. MM_CP_TRY_CHANGE_WRITABLE makes
> entries writable again if a write fault would only set the write bit.
> 
> However, change_huge_pud() ignores the flag. For example, device DAX
> mappings are write-notified once soft-dirty tracking is armed through
> /proc/pid/clear_refs, and a protection change then leaves dirty PUDs
> read-only, so the next write to each of them faults.
> 
> Fix this by adding can_change_pud_writable(), based on
> can_change_pmd_writable(). It omits the NUMA and uffd-wp checks, as
> change_huge_pud() bails out on those changes.
> 
> Signed-off-by: Carlos López <clopez@suse.de>

Sashiko has reviewed this patch and found no issues.

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