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

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Message-ID: <20110914124917.GS5795@redhat.com>
Date:	Wed, 14 Sep 2011 08:49:17 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	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 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.

Ah. Like a touch_nmi_watchdog() type of thing.  Interesting.  I'll poke
around the idle code.  Need to instrument a reproducer first.

Thanks,
Don
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