linux-kernel - Re: [PATCH 08/13] xen/pvticketlock: disable interrupts while blocking

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Message-ID: <4E70C1BE.7060209@redhat.com>
Date:	Wed, 14 Sep 2011 18:01:18 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Don Zickus <dzickus@...hat.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...nel.dk>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	KVM <kvm@...r.kernel.org>,
	Xen Devel <xen-devel@...ts.xensource.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>
Subject: Re: [PATCH 08/13] xen/pvticketlock: disable interrupts while blocking

On 09/14/2011 05:49 PM, Andi Kleen wrote:
> On Wed, Sep 14, 2011 at 10:00:07AM +0300, Avi Kivity wrote:
> >  On 09/13/2011 10:21 PM, Don Zickus wrote:
> >  >Or are you saying an NMI in an idle system will have the same %rip thus
> >  >falsely detecting a back-to-back NMI?
> >  >
> >  >
> >
> >  That's easy to avoid - insert an instruction zeroing the last nmi_rip
> >  somewhere before or after hlt.  It's always okay to execute such an
> >  instruction (outside the nmi handler itself), since nmi_rip is meant to
> >  detect a "no instructions executed" condition.
>
> At least for classic hlt there is no simple "after hlt" because it's all
> interrupt handlers and exceptions and everything else that can interrupt
> combined.

If an NMI hits in an interrupt handler, or in the "after hlt" section 
before the write-to-last-nmi-rip, then we'll see that %rip has changed.  
If it hits after the write-to-last-nmi-rip instruction (or in the hlt 
itself), then we'll also see that %rip has changed, due to the effect of 
that instruction.

-- 
error compiling committee.c: too many arguments to function

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