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Date: Wed, 14 Sep 2011 10:00:07 +0300
From: Avi Kivity <avi@redhat.com>
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To: Don Zickus <dzickus@redhat.com>
CC: Andi Kleen <andi@firstfloor.org>, Jeremy Fitzhardinge <jeremy@goop.org>,
        Peter Zijlstra <peterz@infradead.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ingo Molnar <mingo@elte.hu>, the arch/x86 maintainers <x86@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Nick Piggin <npiggin@kernel.dk>, Marcelo Tosatti <mtosatti@redhat.com>,
        KVM <kvm@vger.kernel.org>, Xen Devel <xen-devel@lists.xensource.com>,
        Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>,
        Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Subject: Re: [PATCH 08/13] xen/pvticketlock: disable interrupts while blocking
References: <20110906182758.GR5795@redhat.com> <4E66EF86.9070200@redhat.com> <20110907134411.GV5795@redhat.com> <4E678992.5050709@redhat.com> <20110907155657.GX5795@redhat.com> <4E679AF4.50209@redhat.com> <20110907165203.GQ6838@redhat.com> <4E67A551.4000502@redhat.com> <20110913184044.GN5795@redhat.com> <20110913190320.GR7761@one.firstfloor.org> <20110913192152.GO5795@redhat.com>
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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.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.