Thread (8 messages) 8 messages, 2 authors, 2019-09-20

Re: [PATCH v5 3/3] mm: fix double page fault on arm64 if PTE_AF is cleared

From: Catalin Marinas <catalin.marinas@arm.com>
Date: 2019-09-19 16:42:14
Also in: linux-mm, lkml

On Fri, Sep 20, 2019 at 12:12:04AM +0800, Jia He wrote:
quoted hunk ↗ jump to hunk
@@ -2152,7 +2163,29 @@ static inline void cow_user_page(struct page *dst, struct page *src, unsigned lo
 	 */
 	if (unlikely(!src)) {
 		void *kaddr = kmap_atomic(dst);
-		void __user *uaddr = (void __user *)(va & PAGE_MASK);
+		void __user *uaddr = (void __user *)(addr & PAGE_MASK);
+		pte_t entry;
+
+		/* On architectures with software "accessed" bits, we would
+		 * take a double page fault, so mark it accessed here.
+		 */
+		if (arch_faults_on_old_pte() && !pte_young(vmf->orig_pte)) {
+			spin_lock(vmf->ptl);
+			if (likely(pte_same(*vmf->pte, vmf->orig_pte))) {
+				entry = pte_mkyoung(vmf->orig_pte);
+				if (ptep_set_access_flags(vma, addr,
+							  vmf->pte, entry, 0))
+					update_mmu_cache(vma, addr, vmf->pte);
+			} else {
+				/* Other thread has already handled the fault
+				 * and we don't need to do anything. If it's
+				 * not the case, the fault will be triggered
+				 * again on the same address.
+				 */
+				return -1;
+			}
+			spin_unlock(vmf->ptl);
Returning with the spinlock held doesn't normally go very well ;).

-- 
Catalin

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