linux-kernel - Re: [PATCH 6/7] x86, xsave: disable xsave in i387 emulation mode

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Date:	Wed, 21 Jul 2010 11:16:02 -0700
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	Robert Richter <robert.richter@....com>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/7] x86, xsave: disable xsave in i387 emulation mode

On Wed, 2010-07-21 at 10:03 -0700, Robert Richter wrote:
> xsave is broken for (!HAVE_HWFP). This is the case if config
> MATH_EMULATION is enabled, 'no387' kernel parameter is set and xsave
> exists. xsave will not work because x86/math-emu and xsave share the
> same memory. As this case can be treated as corner case we simply
> disable xsave then.

I think it is cleaner to clear these cpu capabilities in the function
which handles no387 boot parameter.

Otherwise Acked-by: Suresh Siddha <suresh.b.siddha@...el.com>

thanks.

> 
> Signed-off-by: Robert Richter <robert.richter@....com>
> ---
>  arch/x86/kernel/i387.c |    6 ++++++
>  1 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
> index e73c54e..ff81143 100644
> --- a/arch/x86/kernel/i387.c
> +++ b/arch/x86/kernel/i387.c
> @@ -67,6 +67,12 @@ static void __cpuinit init_thread_xstate(void)
>  	 */
>  
>  	if (!HAVE_HWFP) {
> +		/*
> +		 * Disable xsave as we do not support it if i387
> +		 * emulation is enabled.
> +		 */
> +		setup_clear_cpu_cap(X86_FEATURE_XSAVE);
> +		setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
>  		xstate_size = sizeof(struct i387_soft_struct);
>  		return;
>  	}

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