linux-kernel - Re: [RFC PATCH 01/11] x86,fpu: document the data structures a little

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Date:	Mon, 12 Jan 2015 22:18:02 +0100
From:	Borislav Petkov <bp@...e.de>
To:	riel@...hat.com
Cc:	linux-kernel@...r.kernel.org, mingo@...hat.com, hpa@...or.com,
	matt.fleming@...el.com, oleg@...hat.com, pbonzini@...hat.com,
	tglx@...utronix.de, luto@...capital.net
Subject: Re: [RFC PATCH 01/11] x86,fpu: document the data structures a little

On Sun, Jan 11, 2015 at 04:46:23PM -0500, riel@...hat.com wrote:
> From: Rik van Riel <riel@...hat.com>
> 
> Add some documentation to data structures used for FPU context
> switching.
> 
> Signed-off-by: Rik van Riel <riel@...hat.com>
> ---
>  arch/x86/include/asm/processor.h | 9 +++++++--
>  arch/x86/kernel/cpu/common.c     | 1 +
>  2 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index a092a0c..17bd8a0 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -400,6 +400,11 @@ struct xsave_struct {
>  	/* new processor state extensions will go here */
>  } __attribute__ ((packed, aligned (64)));
>  
> +/*
> + * The FPU state used depends on the capabilities of the hardware; the
> + * registers used for vector instructions on newer hardware are included
> + * in the FPU state.
> + */
>  union thread_xstate {
>  	struct i387_fsave_struct	fsave;
>  	struct i387_fxsave_struct	fxsave;
> @@ -408,8 +413,8 @@ union thread_xstate {
>  };
>  
>  struct fpu {
> -	unsigned int last_cpu;
> -	unsigned int has_fpu;
> +	unsigned int last_cpu;		/* FPU state last loaded on this CPU */

Isn't that the last CPU which had the FPU?

> +	unsigned int has_fpu;		/* FPU state in current use on CPU */

I understand ->has_fpu as this thread has the FPU. See comment over
user_has_fpu().

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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