linux-kernel - [PATCH 0/1] x86/fpu: x86/fpu: avoid math_state_restore() without used_math() in __restore_xstate

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Date:	Sat, 7 Mar 2015 16:38:24 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Dave Hansen <dave.hansen@...el.com>, Borislav Petkov <bp@...e.de>,
	Ingo Molnar <mingo@...nel.org>
Cc:	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: [PATCH 0/1] x86/fpu: x86/fpu: avoid math_state_restore() without
	used_math() in __restore_xstate_sig()

On 03/05, Oleg Nesterov wrote:
>
> The patch is horrible, yes. But simple, and math_state_restore/init_fpu
> are already horrible and need the cleanups.

OK, nobody liked it. How about this one for stable?

Ingo, Linus, Andy. I do agree, math_state_restore() should be called with
irqs enabled. And I was going to do this too. But this is wrong without
other changed. I hope I send them soon.

We need to remove this !tsk_used_math() code from math_state_restore().
And init_fpu() should die. Just look at __restore_xstate_sig() changed
by this patch. Why does it call init_fpu() ? We only need fpu_alloc().
fpu_finit() is pointless, we are going to overwrite fpu->state. used_math()
makes no sense at this point. user_fpu_begin() and math_state_restore()
should set this flag. And other changes.

Could you please review?

Oleg.

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