Re: problem wit svm_get_msr on kvm-kmod-2.6.31.6

[Jan Kiszka <jan.kiszka@siemens.com>]

Avi Kivity wrote:
> On 11/17/2009 11:59 AM, Jan Kiszka wrote:
>> Jan Kiszka wrote:
>>    
>>> Dietmar Maurer wrote:
>>>      
>>>> Hi Jan,
>>>>
>>>> The ubuntu code puts some barrier around the read.
>>>>
>>>> http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-hardy.git;a=commitdiff;h=198b348d96c9769153e72ca2461f8d841ddff1cc
>>>>
>>>> You simply override this with your own code - without barrier. Do you think this is correct?
>>>>        
>>> Unless I messed it up again, I "overwrote" it with what is in latest
>>> mainline regarding native_read_tsc. But I will check once more.
>>>      
>> The removal of those barriers came with
>> 0d12cdd5f883f508d33b85c1bae98fa28987c8c7 (sched: improve sched_clock()
>> performance). So this is now an upstream question:
>>
>> Do we bother about the precision of native_read_tsc in svm or not?
>>
>>    
> 
> I doubt it matters.  rdtsc will be followed by a return to the guest or 
> userspace, either of which is expensive enough to swamp any speculation.
> 

Right. So the kvm-kmod replacement is also fine.

Dietmar, if you could confirm that your issue is fixed, I would roll out
a kvm-kmod-2.6.31.6b, likely the last version of this series. The .32
series will be updated on 2.6.32-final or the next KVM-affecting -rc
release.

Jan

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