From: Linus Torvalds <torvalds@g5.osdl.org>
Date: Tue, 29 Nov 2005 22:07:55 +0000 (-0800)
Subject: cow_user_page: fix page alignment
X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=5d2a2dbbc1025dbf7998b9289574d9592b8f21cc;p=openwrt%2Fstaging%2Fblogic.git

cow_user_page: fix page alignment

High Dickins points out that the user virtual address passed to the page
fault handler isn't necessarily page-aligned.

Also, add a comment on why the copy could fail for the user address case.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---

diff --git a/mm/memory.c b/mm/memory.c
index 74f95ae0510b..745b3482e6c2 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1394,8 +1394,15 @@ static inline void cow_user_page(struct page *dst, struct page *src, unsigned lo
 	 */
 	if (unlikely(!src)) {
 		void *kaddr = kmap_atomic(dst, KM_USER0);
-		unsigned long left = __copy_from_user_inatomic(kaddr, (void __user *)va, PAGE_SIZE);
-		if (left)
+		void __user *uaddr = (void __user *)(va & PAGE_MASK);
+
+		/*
+		 * This really shouldn't fail, because the page is there
+		 * in the page tables. But it might just be unreadable,
+		 * in which case we just give up and fill the result with
+		 * zeroes.
+		 */
+		if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE))
 			memset(kaddr, 0, PAGE_SIZE);
 		kunmap_atomic(kaddr, KM_USER0);
 		return;