linux-kernel - Re: [ 174/262] x86, avx: dont use avx instructions with "noxsave" boot param

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Date:	Sun, 07 Oct 2012 22:26:12 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Suresh Siddha <suresh.b.siddha@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	alan@...rguk.ukuu.org.uk,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [ 174/262] x86, avx: dont use avx instructions with "noxsave"
 boot param

On Fri, 2012-09-28 at 11:51 -0700, Greg Kroah-Hartman wrote:
> From: Greg KH <gregkh@...uxfoundation.org>
> 
> 3.5-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Suresh Siddha <suresh.b.siddha@...el.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@...el.com>
> Link: http://lkml.kernel.org/r/1343755754.2041.2.camel@sbsiddha-desk.sc.intel.com
> Signed-off-by: H. Peter Anvin <hpa@...or.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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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