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x86, pat: Fix set_memory_wc related corruption 

Changeset 3869c4aa18
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 <glisse@freedesktop.org>
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
LKML-Reference: <20090730214319.GA1889@linux-os.sc.intel.com>
Acked-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
Pallipadi, Venkatesh 2009-07-30 14:43:19 -07:00 committed by H. Peter Anvin
parent 0e83815be7
commit bdc6340f4e
1 changed files with 6 additions and 3 deletions
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9
arch/x86/mm/pageattr.c
View File

@ -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;
}