[PATCH v2 01/46] hugetlb: don't set PageUptodate for UFFDIO_CONTINUE

[James Houghton]

If would be bad if we actually set PageUptodate with UFFDIO_CONTINUE;
PageUptodate indicates that the page has been zeroed, and we don't want
to give a non-zeroed page to the user.

The reason this change is being made now is because UFFDIO_CONTINUEs on
subpages definitely shouldn't set this page flag on the head page.

Signed-off-by: James Houghton <jthoughton@xxxxxxxxxx>

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 07abcb6eb203..792cb2e67ce5 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6256,7 +6256,16 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
 	 * preceding stores to the page contents become visible before
 	 * the set_pte_at() write.
 	 */
-	__folio_mark_uptodate(folio);
+	if (!is_continue)
+		__folio_mark_uptodate(folio);
+	else if (!folio_test_uptodate(folio)) {
+		/*
+		 * This should never happen; HugeTLB pages are always Uptodate
+		 * as soon as they are allocated.
+		 */
+		ret = -EFAULT;
+		goto out_release_nounlock;
+	}
 
 	/* Add shared, newly allocated pages to the page cache. */
 	if (vm_shared && !is_continue) {
-- 
2.39.2.637.g21b0678d19-goog