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SubjectRe: [ 174/262] x86, avx: dont use avx instructions with "noxsave" boot param
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On Fri, 2012-09-28 at 11:51 -0700, Greg Kroah-Hartman wrote:
> From: Greg KH <gregkh@linuxfoundation.org>
>
> 3.5-stable review patch. If anyone has any objections, please let me know.
>
> ------------------
>
> From: Suresh Siddha <suresh.b.siddha@intel.com>
>
> commit c6fd893da927c6cefb2ece22402765379921a834 upstream.
>
> Clear AVX, AVX2 features along with clearing XSAVE feature bits,
> as part of the parsing "noxsave" parameter.
>
> Fixes the kernel boot panic with "noxsave" boot parameter.
>
> We could have checked cpu_has_osxsave along with cpu_has_avx etc, but Peter
> mentioned clearing the feature bits will be better for uses like
> static_cpu_has() etc.

This was marked as needed for 3.5 only - presumably because the kernel
wasn't using AVX before this - but don't we also need to clear these
bits even in earlier versions so userland knows not to use it?

Ben.

> Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
> Link: http://lkml.kernel.org/r/1343755754.2041.2.camel@sbsiddha-desk.sc.intel.com
> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>
> ---
> arch/x86/kernel/cpu/common.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -144,6 +144,8 @@ static int __init x86_xsave_setup(char *
> {
> setup_clear_cpu_cap(X86_FEATURE_XSAVE);
> setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
> + setup_clear_cpu_cap(X86_FEATURE_AVX);
> + setup_clear_cpu_cap(X86_FEATURE_AVX2);
> return 1;
> }
> __setup("noxsave", x86_xsave_setup);


--
Ben Hutchings
You can't have everything. Where would you put it?
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