linux-kernel - Re: intel_pstate divide error with v3.13-rc4-256-gb7000ad

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Date:	Fri, 27 Dec 2013 17:17:38 +0000
From:	"Richard W.M. Jones" <rjones@...hat.com>
To:	Gleb Natapov <gleb@...nel.org>
Cc:	Kashyap Chamarthy <kchamart@...hat.com>,
	Josh Boyer <jwboyer@...oraproject.org>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Dirk Brandewie <dirk.brandewie@...il.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>
Subject: Re: intel_pstate divide error with v3.13-rc4-256-gb7000ad

On Fri, Dec 27, 2013 at 07:01:48PM +0200, Gleb Natapov wrote:
> On Fri, Dec 27, 2013 at 06:52:48PM +0200, Gleb Natapov wrote:
> > On Fri, Dec 27, 2013 at 03:15:39PM +0100, Kashyap Chamarthy wrote:
> > > [. . .]
> > > 
> > > >> KVM does not emulate P-states at all. intel_pstate_init() calls
> > > >> intel_pstate_msrs_not_valid() before printing "Intel P-state driver
> > > >> initializing."  which suppose to fail since it checks that two reads of
> > > >> MSR_IA32_APERF return different values, but KVM does not emulate this msr
> > > >> at all, so both calls should return zero (KVM suppose to inject #GP, all rdmsrl
> > > >> are patched to be rdmsrl_safe in a guest).
> > > >>
> > > >> Anything interesting in host dmesg?
> > > 
> > > Heya Gleb,
> > > 
> > > Here's the relevant dmesg snippet (full dmesg, refer the attachment below):
> > That's guest dmesg. What about host one? Can you ftrace the failure?
> > 
> Ugh, it looks like guest dmesg but there are KVM messages there too ("[
> 281.443662] kvm [2452]: vcpu0 unhandled rdmsr: 0xe8" is unhandled access
> to MSR_IA32_APERF I was talking about above), so I guess this is nested
> guest invocation?  Does it happen in non nested guest?

FWIW I could not reproduce the reported bug.  I am also using a guest
for testing, but *not* using nested KVM.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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