linux-kernel - Re: [PATCH 1/1] x86/fpu: x86/fpu: avoid math_state_restore() without used_math() in __restore_xstate

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Message-ID: <20150309165338.GF12732@pd.tnic>
Date:	Mon, 9 Mar 2015 17:53:38 +0100
From:	Borislav Petkov <bp@...e.de>
To:	Oleg Nesterov <oleg@...hat.com>
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 1/1] x86/fpu: x86/fpu: avoid math_state_restore() without
 used_math() in __restore_xstate_sig()

On Mon, Mar 09, 2015 at 05:24:04PM +0100, Oleg Nesterov wrote:
> Well, this is the same thinhg reported by Dave ;)

Am I the only one in thinking that this FPU thing went completely nuts?!
Just kill it all and let's start from scratch. :-P

> It is not fixed by Quentin's patch.
> 
> This patch "fixes" the problem in a sense that the kernel won't crash
> after restore_fpu_checking() triggers #GP. Before this patch
> do_general_protection()->fixup_exception() does not work in this case
> and the kernel panics.
> 
> But restore_fpu_checking() should not trigger #GP (and fail).

Right.

...

> But this too doesn't fix the problem: fpu_finit() is buggy on Dave's
> machine.

In talking about fpu_finit() - I still have two cleanup patches queued
from you:

http://git.kernel.org/cgit/linux/kernel/git/bp/bp.git/log/?h=tip-x86-fpu-2

Thanks.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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