patch mm-flush-dcache-before-writing-into-page-to-avoid-alias.patch added to 2.6.32-stable tree

This is a note to let you know that we have just queued up the patch titled

Subject: mm: flush dcache before writing into page to avoid alias

to the 2.6.32-stable tree. Its filename is

mm-flush-dcache-before-writing-into-page-to-avoid-alias.patch

A git repo of this tree can be found at
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

From 931e80e4b3263db75c8e34f078d22f11bbabd3a3 Mon Sep 17 00:00:00 2001
From: anfei zhou <[email protected]>
Date: Tue, 2 Feb 2010 13:44:02 -0800
Subject: mm: flush dcache before writing into page to avoid alias

From: anfei zhou <[email protected]>

commit 931e80e4b3263db75c8e34f078d22f11bbabd3a3 upstream.

The cache alias problem will happen if the changes of user shared mapping is not flushed before copying, then user and kernel mapping may be mapped into two different cache line, it is impossible to guarantee the coherence after iov_iter_copy_from_user_atomic. So the right steps should be:

	flush_dcache_page(page);
	kmap_atomic(page);
	write to page;
	kunmap_atomic(page);
	flush_dcache_page(page);

More precisely, we might create two new APIs flush_dcache_user_page and flush_dcache_kern_page to replace the two flush_dcache_page accordingly.

Here is a snippet tested on omap2430 with VIPT cache, and I think it is not ARM-specific:

	int val = 0x11111111;
	fd = open("abc", O_RDWR);
	addr = mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
	*(addr+0) = 0x44444444;
	tmp = *(addr+0);
	*(addr+1) = 0x77777777;
	write(fd, &val, sizeof(int));
	close(fd);

The results are not always 0x11111111 0x77777777 at the beginning as expected. Sometimes we see 0x44444444 0x77777777.

---
 fs/fuse/file.c |    3 +++
 mm/filemap.c   |    3 +++
 2 files changed, 6 insertions(+)

@@ -828,6 +828,9 @@ static ssize_t fuse_fill_write_pages(str
 		if (!page)
 			break;
 
+		if (mapping_writably_mapped(mapping))
+			flush_dcache_page(page);
+
 		pagefault_disable();
 		tmp = iov_iter_copy_from_user_atomic(page, ii, offset, bytes);
 		pagefault_enable();

@@ -2253,6 +2253,9 @@ again:
 		if (unlikely(status))
 			break;
 
+		if (mapping_writably_mapped(mapping))
+			flush_dcache_page(page);
+
 		pagefault_disable();
 		copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
 		pagefault_enable();

Patches currently in stable-queue which might be from [email protected] are