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Date: Thu, 18 Nov 2010 13:51:44 -0600 From: Jason Wessel <jason.wessel@...driver.com> To: Don Zickus <dzickus@...hat.com> CC: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>, Robert Richter <robert.richter@....com>, ying.huang@...el.com, Andi Kleen <andi@...stfloor.org>, LKML <linux-kernel@...r.kernel.org>, Frederic Weisbecker <fweisbec@...il.com> Subject: Re: [V2 PATCH 0/6] x86, NMI: give NMI handler a face-lift On 11/18/2010 01:32 PM, Don Zickus wrote: > On Thu, Nov 18, 2010 at 02:17:12PM +0100, Peter Zijlstra wrote: > >> On Thu, 2010-11-18 at 06:47 -0600, Jason Wessel wrote: >> >>> More specifically >>> when another subsystem injects an NMI event the perf NMI code returns >>> NOTIFY_STOP. >>> >> Not unconditionally, right? We only do so when the previous NMI was from >> the PMU and nobody claimed this one (NOTIFY_STOP from DIE_NMIUNKNOWN). >> >> Or are you hitting the other one, where !handled but pmu_nmi.handled > >> 1 ? >> > > I think the problem with the virt stuff is that it emulates 0 to the > rdmsrl calls. All platforms except perf_events_intel.c rely on checking > the high bit of the counter register to not be zero, otherwise the code > thinks it crossed zero and triggered an PMI. > > The intel code is a litte smarter and relies on the interrupt logic and > thus doesn't have this problem (to clarify only core2 and later use this, > p4 and p6 use the old methods). > > So the problem is when the nmi watchdog is enabled, the perf event is > 'active' and thus tries to read the counter value. Because it is always > zero, perf just assumes the counter overflowed and the NMI is his. > > Not sure how to fix it yet, other than include the logic that detects we > are on a guest and disable perf?? > > I highly doubt we want to disable perf. I would rather use the source and fix the nmi emulation in KVM/Qemu after we hear back the results from Cyril because it sounds as if the problem is nearly bottomed out. I have no problem what so ever updating kvm / qemu if that is final place we need some fixes. Thanks, Jason. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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