linux-kernel - Re: [PATCH 3/8] x86, i387.c: thread xstate is initialized only on BSP once

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Date:	Wed, 5 Oct 2011 20:49:54 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Fenghua Yu <fenghua.yu@...el.com>
cc:	Ingo Molnar <mingo@...e.hu>, H Peter Anvin <hpa@...or.com>,
	Zwane Mwaikambo <zwane@....linux.org.uk>,
	Tony Luck <tony.luck@...el.com>,
	Asit K Mallick <asit.k.mallick@...el.com>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Len Brown <lenb@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/8] x86, i387.c: thread xstate is initialized only on
 BSP once

On Wed, 5 Oct 2011, Fenghua Yu wrote:

> From: Fenghua Yu <fenghua.yu@...el.com>
> 
> init_thread_xstate() is only called on BSP once to avoid to override
> xstate_size.
> 
> Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> ---
>  arch/x86/kernel/i387.c |    9 ++++++++-
>  1 files changed, 8 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
> index 739d859..de2b48a 100644
> --- a/arch/x86/kernel/i387.c
> +++ b/arch/x86/kernel/i387.c
> @@ -93,6 +93,7 @@ void __cpuinit fpu_init(void)
>  {
>  	unsigned long cr0;
>  	unsigned long cr4_mask = 0;
> +	static int once;
>  
>  	if (cpu_has_fxsr)
>  		cr4_mask |= X86_CR4_OSFXSR;
> @@ -107,8 +108,14 @@ void __cpuinit fpu_init(void)
>  		cr0 |= X86_CR0_EM;
>  	write_cr0(cr0);
>  
> -	if (!smp_processor_id())
> +	/*
> +	 * init_thread_xstate is only called on BSP once to avoid to override
> +	 * xstate_size.
> +	 */
> +	if (!smp_processor_id() && once) {

Brilliant change. Makes sure that init_thread_xstate() is NEVER
called. Was this crap tested at all?

> +		once = 0;
>  		init_thread_xstate();
> +	}
>  
>  	mxcsr_feature_mask_init();
>  	/* clean state in init */
> -- 
> 1.6.0.3
> 
> 
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