Re: [PATCH] arm64: contpte: fix set_access_flags() no-op check for SMMU/ATS faults

On Wed, Mar 04, 2026 at 12:20:31PM +0000, Ryan Roberts wrote:

quoted

 static int __cont_access_flags_changed(pte_t *ptep, pte_t pte, int ncontig)
 {
+	const pteval_t access_mask = PTE_RDONLY | PTE_AF | PTE_WRITE | PTE_DIRTY;
+	pteval_t pte_access = pte_val(pte) & access_mask;
 	int i;
 
-	if (pte_write(pte) != pte_write(__ptep_get(ptep)))
-		return 1;
-
 	for (i = 0; i < ncontig; i++) {
-		pte_t orig_pte = __ptep_get(ptep + i);
-
-		if (pte_dirty(pte) != pte_dirty(orig_pte))
-			return 1;
-
-		if (pte_young(pte) != pte_young(orig_pte))
+		if ((pte_val(__ptep_get(ptep + i)) & access_mask) != pte_access)
 			return 1;
 	}

I think, based on all the above, the current version is actually not buggy. But
I'm only willing to go to 95% confidence :)

If I understand it right James already found and fixed a case that
violated the invariant right? Maybe it is wise to be robust since
things lock up if it goes wrong.

Jason