linux-kernel - Re: [kvm-devel] Guest kernel hangs in smp kvm for older kernels prior to tsc sync cleanup

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Message-ID: <47693054.20501@qumranet.com>
Date:	Wed, 19 Dec 2007 16:53:08 +0200
From:	Avi Kivity <avi@...ranet.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Avi Kivity <avi@...ranet.com>,
	kvm-devel <kvm-devel@...ts.sourceforge.net>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [kvm-devel] Guest kernel hangs in smp kvm for older kernels	prior
 to tsc sync cleanup

Ingo Molnar wrote:
> * Avi Kivity <avi@...ranet.com> wrote:
>
>   
>> Avi Kivity wrote:
>>     
>>>  Testing shows wrmsr and rdtsc function normally.
>>>
>>> I'll try pinning the vcpus to cpus and see if that helps.
>>>
>>>       
>> It does.
>>     
>
> do we let the guest read the physical CPU's TSC? That would be trouble.
>
>   

vmx (and svm) allow us to add an offset to the physical tsc.  We set it
on startup to -tsc (so that an rdtsc on boot would return 0), and
massage it on vcpu migration so that guest rdtsc is monotonic.

The net effect is that tsc on a vcpu can experience large forward jumps
and changes in rate, but no negative jumps.

-- 
error compiling committee.c: too many arguments to function
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