From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Kyle Huey <me@kylehuey.com>
Cc: Kevin Tian <kevin.tian@intel.com>, Wei Liu <wei.liu2@citrix.com>,
Jun Nakajima <jun.nakajima@intel.com>,
xen-devel@lists.xen.org, Jan Beulich <JBeulich@suse.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Robert O'Callahan <robert@ocallahan.org>
Subject: Re: [PATCH v3 2/2] x86/Intel: virtualize support for cpuid faulting
Date: Thu, 20 Oct 2016 15:11:05 +0100 [thread overview]
Message-ID: <69f84011-05db-20ee-39d5-217416461ddc@citrix.com> (raw)
In-Reply-To: <CAP045Aqvd7XYgfxz0ikztnRcXmazyFgU-Du2g-qujM1NYiDj7A@mail.gmail.com>
On 20/10/16 14:55, Kyle Huey wrote:
>
>>> That said, rr currently does not work in Xen guests due to some PMU
>>> issues that we haven't tracked down yet.
>> Is this RR trying to use vPMU and it not functioning, or not
>> specifically trying to use PMU facilities and getting stuck anyway?
> The latter. rr relies on the values returned by the PMU (the retired
> conditional branches counter in particular) being exactly the same
> during the recording and replay phases. This is true when running on
> bare metal, and when running inside a KVM guest, but when running in a
> Xen HVM guest we see values that are off by a branch or two on a small
> fraction of our tests. Since it works in KVM I suspect this is some
> sort of issue with how Xen multiplexes the real PMU and events are
> "leaking" between guests (or perhaps from Xen itself, though I don't
> think the Xen kernel executes any ring 3 code). Even if that's
> correct we're a long way from tracking it down and patching it though.
Hmm. That is unfortunate, and does point towards a bug in Xen. Are
these tests which notice the problem easy to run?
Boris (CC'd) is the maintainer of that code. It has undergone quite a
few changes recently.
~Andrew
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next prev parent reply other threads:[~2016-10-20 14:11 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-14 19:47 [PATCH v3] x86/Intel: virtualize support for cpuid faulting Kyle Huey
2016-10-14 19:47 ` [PATCH v3 1/2] x86/Intel: Expose cpuid_faulting_enabled so it can be used elsewhere Kyle Huey
2016-10-17 12:35 ` Andrew Cooper
2016-10-17 12:43 ` Wei Liu
2016-10-14 19:47 ` [PATCH v3 2/2] x86/Intel: virtualize support for cpuid faulting Kyle Huey
2016-10-17 12:32 ` Wei Liu
2016-10-20 5:10 ` Kyle Huey
2016-10-20 7:56 ` Andrew Cooper
2016-10-20 13:55 ` Kyle Huey
2016-10-20 14:11 ` Andrew Cooper [this message]
2016-10-20 14:40 ` Boris Ostrovsky
2016-10-21 15:52 ` Kyle Huey
2016-10-24 4:18 ` Kyle Huey
2016-10-24 15:05 ` Boris Ostrovsky
2016-10-24 19:22 ` Kyle Huey
2016-10-24 21:15 ` Boris Ostrovsky
2016-10-17 12:49 ` Andrew Cooper
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