From bdc6340f4eb68295b1e7c0ade2356b56dca93d93 Mon Sep 17 00:00:00 2001 From: "Pallipadi, Venkatesh" Date: Thu, 30 Jul 2009 14:43:19 -0700 Subject: [PATCH] x86, pat: Fix set_memory_wc related corruption Changeset 3869c4aa18835c8c61b44bd0f3ace36e9d3b5bd0 that went in after 2.6.30-rc1 was a seemingly small change to _set_memory_wc() to make it complaint with SDM requirements. But, introduced a nasty bug, which can result in crash and/or strange corruptions when set_memory_wc is used. One such crash reported here http://lkml.org/lkml/2009/7/30/94 Actually, that changeset introduced two bugs. * change_page_attr_set() takes &addr as first argument and can the addr value might have changed on return, even for single page change_page_attr_set() call. That will make the second change_page_attr_set() in this routine operate on unrelated addr, that can eventually cause strange corruptions and bad page state crash. * The second change_page_attr_set() call, before setting _PAGE_CACHE_WC, should clear the earlier _PAGE_CACHE_UC_MINUS, as otherwise cache attribute will not be WC (will be UC instead). The patch below fixes both these problems. Sending a single patch to fix both the problems, as the change is to the same line of code. The change to have a addr_copy is not very clean. But, it is simpler than making more changes through various routines in pageattr.c. A huge thanks to Jerome for reporting this problem and providing a simple test case that helped us root cause the problem. Reported-by: Jerome Glisse Signed-off-by: Venkatesh Pallipadi Signed-off-by: Suresh Siddha LKML-Reference: <20090730214319.GA1889@linux-os.sc.intel.com> Acked-by: Dave Airlie Signed-off-by: H. Peter Anvin --- arch/x86/mm/pageattr.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c index 1b734d7a8966..895d90e1a81b 100644 --- a/arch/x86/mm/pageattr.c +++ b/arch/x86/mm/pageattr.c @@ -997,12 +997,15 @@ EXPORT_SYMBOL(set_memory_array_uc); int _set_memory_wc(unsigned long addr, int numpages) { int ret; + unsigned long addr_copy = addr; + ret = change_page_attr_set(&addr, numpages, __pgprot(_PAGE_CACHE_UC_MINUS), 0); - if (!ret) { - ret = change_page_attr_set(&addr, numpages, - __pgprot(_PAGE_CACHE_WC), 0); + ret = change_page_attr_set_clr(&addr_copy, numpages, + __pgprot(_PAGE_CACHE_WC), + __pgprot(_PAGE_CACHE_MASK), + 0, 0, NULL); } return ret; }