linux-kernel - Re: [PATCH 4/4] x86/fpu: don't abuse drop_init_fpu() in flush

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Message-ID: <20150315200436.GA30079@redhat.com>
Date:	Sun, 15 Mar 2015 21:04:36 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Borislav Petkov <bp@...e.de>
Cc:	Dave Hansen <dave.hansen@...el.com>,
	Ingo Molnar <mingo@...nel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Pekka Riikonen <priikone@....fi>,
	Rik van Riel <riel@...hat.com>,
	Suresh Siddha <sbsiddha@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	Quentin Casasnovas <quentin.casasnovas@...cle.com>
Subject: Re: [PATCH 4/4] x86/fpu: don't abuse drop_init_fpu() in
	flush_thread()

On 03/15, Borislav Petkov wrote:
>
> On Sun, Mar 15, 2015 at 07:16:43PM +0100, Oleg Nesterov wrote:
>
> Anyway, we're on the same page and that was a good exercise :-)

Yes, finally ;)

> +/*
> + * In addition to "forgetting" FPU state for @tsk, we restore the
> + * default FPU state in the eager case. Note, this is not needed in the
> + * non-eager case because there we will set CR0.TS and fault and setup
> + * an FPU state lazily.
> + *
> + * We restore the default FPU state in the eager case here as a means of
> + * addressing the failure of restoring the FPU state which @tsk points
> + * to and we still need some state to use so we use the default, clean
> + * one.
> + */
>  static inline void drop_init_fpu(struct task_struct *tsk)
>  {
>  	if (!use_eager_fpu())

But please note that it is not only used after the failure.
See handle_signal() and the first drop_init_fpu() in __restore_xstate_sig().

I think its name is confusing a bit...

Oleg.

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