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

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Message-ID: <20150305083849.GP4938@chrystal.uk.oracle.com>
Date:	Thu, 5 Mar 2015 09:38:49 +0100
From:	Quentin Casasnovas <quentin.casasnovas@...cle.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Dave Hansen <dave.hansen@...el.com>,
	Quentin Casasnovas <quentin.casasnovas@...cle.com>,
	Andy Lutomirski <luto@...capital.net>,
	Borislav Petkov <bp@...e.de>, 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 Wed, Mar 04, 2015 at 08:06:51PM +0100, Oleg Nesterov wrote:
> On 03/04, Dave Hansen wrote:
> >
> > I'm running a commit from the tip/x86/fpu branch: ae486033b98.  It's on
> > a system which I normally boot with 'noxsaves'.  When I boot without
> > 'noxsaves' it is getting a GPF around the time that init is forked off.
> 
> And I assume that (before this commit) the kernel runs fine if you boot
> without 'noxsaves'?
> 
> > 
> > The full oops is below, but addr2line points to the "alternative_input("
> > line in xrstor_state().
> > 
> > The one that oopses has this in bootup:
> > 
> >    xsave: enabled xstate_bv 0x1f, cntxt size 0x3c0 using compacted form
> > 
> > The one that works says:
> > 
> >    xsave: enabled xstate_bv 0x1f, cntxt size 0x440 using standard form
> > 
> Thanks. I'll try to investigate tomorrow.
> 
> Well, the kernel crashes because xrstor_state() is buggy, Quentin already
> has a fix.
> 
> But #GP should be explained...
> 

Hopefully the couple of fixes to prevent the #GP should be merged soon, but
they only cure the symptoms and not the root cause of this issue, I think.

Quentin
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