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

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Message-ID: <52BDB63B.70107@redhat.com>
Date:	Fri, 27 Dec 2013 18:17:47 +0100
From:	Kashyap Chamarthy <kchamart@...hat.com>
To:	Gleb Natapov <gleb@...nel.org>
CC:	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>,
	"Richard W.M. Jones" <rjones@...hat.com>
Subject: Re: intel_pstate divide error with v3.13-rc4-256-gb7000ad

On 12/27/2013 06:01 PM, 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? 

Here's host dmesg: https://bugzilla.kernel.org/attachment.cgi?id=119751

>> Can you ftrace the failure?

Can try, need some time (rest of the day I'll be away travelling,
will try to do it over the weekend, and update the Kernel
bugzilla with observations).

>>
> 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? 

Yeah -- sorry, I forgot to note it's in a nested environment :(

> Does it happen in non nested guest?

I need to that.

Note to self: Also try with a newer Kernel on the host.



-- 
/kashyap
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