Re: [Qemu-devel] [PATCH] RFC: powerpc: add PVR compatibility check

[Andreas Färber]

Am 05.11.2013 07:05, schrieb Alexander Graf:
> 
> 
> Am 05.11.2013 um 05:00 schrieb Paul Mackerras <address@hidden>:
> 
>> On Mon, Nov 04, 2013 at 10:05:58AM +0100, Alexander Graf wrote:
>>>
>>> Yeah, we really need to check that guest vpcu == host vcpu for HV KVM.
>>
>> In general I agree, but the one difficulty I see is that a check for
>> exact equality will interact badly with qemu's habit of picking a
>> specific processor version when the user specifies something general
>> like "POWER7".  So if the user does -cpu POWER7 on a machine with
>> (for example) a POWER7 v2.1 processor, but qemu arbitrarily picks the
>> PVR for POWER7 v2.3, then it will fail, which will be completely
>> puzzling to the user -- "I asked for POWER7, and it is a POWER7,
>> what's the problem??".
>>
>> Maybe if the user asks for a non-specific processor type, and the
>> host's PVR matches the request, then qemu should take the host's PVR
>> rather than just picking some arbitrary processor version.
> 
> Yup.

But then it's no longer generally reproducible: "POWER7" won't be
"POWER7" on another machine.

One thing I original did iirc was to hide the aliases from QMP. You can
always do stupid things on the command line and then we can blame you,
but if libvirt and upper layers don't offer "POWER7" to the end user
then we don't need to worry about the average user misinterpreting its
semantics.

Andreas

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