On Fri, Nov 20, 2020 at 02:35:52PM +0000, Will Deacon wrote:
pte_accessible() is used by ptep_clear_flush() to figure out whether TLB invalidation is necessary when unmapping pages for reclaim. Although our implementation is correct according to the architecture, returning true only for valid, young ptes in the absence of racing page-table modifications, this is in fact flawed due to lazy invalidation of old ptes in ptep_clear_flush_young() where we elide the expensive DSB instruction for completing the TLB invalidation.
Rather than penalise the aging path, adjust pte_accessible() to return true for any valid pte, even if the access flag is cleared.
Cc: stable@vger.kernel.org Fixes: 76c714be0e5e ("arm64: pgtable: implement pte_accessible()") Reported-by: Yu Zhao yuzhao@google.com Signed-off-by: Will Deacon will@kernel.org
Reviewed-by: Catalin Marinas catalin.marinas@arm.com