Re: [PATCH] x86: Fix set_memory_wc related corruption
From: Dave Airlie
Date: Thu Jul 30 2009 - 20:27:19 EST
On Fri, Jul 31, 2009 at 7:43 AM, Pallipadi,
Venkatesh<venkatesh.pallipadi@xxxxxxxxx> wrote:
>
> 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 <glisse@xxxxxxxxxxxxxxx>
>
> Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx>
> Signed-off-by: Suresh Siddha <suresh.b.siddha@xxxxxxxxx>
Acked-by: Dave Airlie <airlied@xxxxxxxxxx>
please urgent this, so I don't get blamed for radeon KMS not working ;-)
Dave.
> ---
>
> Patch needed for 2.6.30-stable as well
>
> arch/x86/mm/pageattr.c | 9 ++++++---
> 1 files changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
> index 1b734d7..895d90e 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;
> }
> --
> 1.6.0.6
>
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