Re: [PATCH] x86: Fix set_memory_wc related corruption

[Dave Airlie]

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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