linux-kernel - Re: Oops with tip/x86/fpu

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Date:	Thu, 5 Mar 2015 19:46:13 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Dave Hansen <dave.hansen@...el.com>
Cc:	Borislav Petkov <bp@...e.de>,
	Quentin Casasnovas <quentin.casasnovas@...cle.com>,
	Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...nel.org>,
	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>
Subject: Re: Oops with tip/x86/fpu

On 03/05, Dave Hansen wrote:
>
> On 03/05/2015 10:22 AM, Oleg Nesterov wrote:
> > On 03/05, Oleg Nesterov wrote:
> >> I _think_ that the difference is that eager_fpu_init()->xrstor_state()
> >> was called before apply_alternatives(), so it used XRSTOR.
> >>
> >> Note also that (before this commit) restore_fpu_checking() was almost
> >> never called right after init_fpu(). If use_eager_fpu() == T.
> >>
> >> After this commit the first xrstor_state() uses XRSTORS. And that is
> >> how (I think) 'noxsaves' makes the difference.
> >>
> >>
> >> So. I can be easily wrong, but so far I _think_ that this commit disclosed
> >> another problem. And even if I am wrong and this commit is buggy, we need
> >> to understand why ;)
> >>
> >> I'll try to think about debugging patch, I can't reproduce this problem
> >> on my machine...
> >
> > Dave. could please run the test-case below?
> >
> > Without 'noxsaves', and without my commit.
>
> So you want it tested at 4b2e762e2e5 in tip/x86/fpu?

Yes, or even before, this doesn't really matter I think.

Thanks,

Oleg.

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