Re: [PATCH] Emulate MSR_EBC_FREQUENCY_ID

[Jes Sorensen <Jes.Sorensen@redhat.com>]

On 09/09/10 10:29, Jes Sorensen wrote:
> On 09/09/10 10:12, Avi Kivity wrote:
>> From the spec:
>>
>>> 31:24 Core Clock Frequency to System
>>>       Bus Frequency Ratio. (R)
>>>       The processor core clock
>>>       frequency to system bus
>>>       frequency ratio observed at the
>>>       de-assertion of the reset pin.
>>
>> A frequency ratio of 0 might be unexpected by some guests.
> 
> Problem with that one is that it is only for CPU models 2, 3, 4, 6.
> I haven't found a way to distinguish CPU models from within KVM, but
> maybe I am blind?
> 
> Bits 31:24 are invalid on models 0 and 1.

Actually scratch that - the problem is that we are trying to emulate the
MSR because the guest thinks it's valid on the old CPU. However since we
don't know which CPU model the guest was expecting, there really isn't a
valid answer. Setting bits 31:24 to a divisor or 1 would probably be
safe, but there is no guarantee that other guests might not expect the
MSR to return 0 in those bits for other cases.

I can spin a patch that does that, I am just not convinced it's any
safer. Let me know what you prefer.

Jes