Re: [PATCH 29/46] mm/mremap: use pudp_huge_get_and_clear() when moving huge PUDs

[Pedro Falcato]

On Tue, Oct 27, 2026 at 12:17:49AM +0100, David Hildenbrand (Arm) wrote:
> move_huge_pud() reads the old PUD and clears it in separate operations.
> Hardware accessed or dirty updates between those operations can be lost
> when the saved entry is installed at the new address.
> 
> The raw pud_clear() also bypasses page_table_check_pud_clear(), while
> set_pud_at() accounts for the destination mapping. This leaves the
> checker counts unbalanced for mappings tracked by page table checking.
> 
> To fix it, simply use pudp_huge_get_and_clear().
> 
> Fixes: 7d846db7d0e2 ("mm/mremap: convert huge PUD move to separate helper")
> Cc: stable@xxxxxxxxxxxxxxx
> Reviewed-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>
> Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

Reviewed-by: Pedro Falcato <pfalcato@xxxxxxx>

At what point do we ban straight up clearing a PTE/PMD/PUD/etc? :)

-- 
Pedro