linux-kernel - Re: [PATCH 2/6] x86, fpu: remove unnecessary user_fpu_end() in save_xstate

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Date:	Sun, 26 Aug 2012 13:30:01 +0200
From:	Borislav Petkov <bp@...64.org>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	hpa@...or.com, mingo@...nel.org, torvalds@...ux-foundation.org,
	andreas.herrmann3@....com, robert.richter@....com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/6] x86, fpu: remove unnecessary user_fpu_end() in
 save_xstate_sig()

On Fri, Aug 24, 2012 at 02:12:58PM -0700, Suresh Siddha wrote:
> Few lines below we do drop_fpu() which is more safer. Remove the
> unnecessary user_fpu_end() in save_xstate_sig(), which allows
> the drop_fpu() to ignore any pending exceptions from the user-space
> and drop the current fpu.
> 
> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
> ---
>  arch/x86/include/asm/fpu-internal.h |   17 +++--------------
>  arch/x86/kernel/xsave.c             |    1 -
>  2 files changed, 3 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/x86/include/asm/fpu-internal.h b/arch/x86/include/asm/fpu-internal.h
> index fe95ad0..fac39e9 100644
> --- a/arch/x86/include/asm/fpu-internal.h
> +++ b/arch/x86/include/asm/fpu-internal.h
> @@ -412,22 +412,11 @@ static inline void __drop_fpu(struct task_struct *tsk)
>  }
>  
>  /*
> - * The actual user_fpu_begin/end() functions
> - * need to be preemption-safe.
> + * Need to be preemption-safe.
>   *
> - * NOTE! user_fpu_end() must be used only after you
> - * have saved the FP state, and user_fpu_begin() must
> - * be used only immediately before restoring it.
> - * These functions do not do any save/restore on
> - * their own.
> + * NOTE! user_fpu_begin() must be used only immediately before restoring
> + * it. This function does not do any save/restore on their own.
>   */
> -static inline void user_fpu_end(void)
> -{
> -	preempt_disable();
> -	__thread_fpu_end(current);
> -	preempt_enable();
> -}

Now that user_fpu_begin has lost its counterpart user_fpu_end, maybe
rename it to user_fpu_init() or something similar which doesn't suggest
there's a _begin and an _end thingy?

Thanks.

-- 
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
Einsteinring 24, 85609 Dornach
GM: Alberto Bozzo
Reg: Dornach, Landkreis Muenchen
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