Re: [Qemu-ppc] [Qemu-devel] [RFC PATCH] powerpc: add PVR mask support

[Andreas Färber]

Am 15.08.2013 17:30, schrieb Alexander Graf:
> 
> On 15.08.2013, at 17:11, Andreas Färber wrote:
> 
>> Am 15.08.2013 15:12, schrieb Anthony Liguori:
>>> Everyone is talking past each other and no one is addressing the real
>>> problem.  There are two distinct issues here:
>>>
>>> 1) We have two ABIs that cannot be changed unless there's a very good
>>>   reason to.  Alexey's original patch breaks both.  The guest ABI
>>>   cannot change given a fixed command line.
>>>
>>>   IOW, the exposed PVR value for -cpu POWER7 cannot change across
>>>   versions of QEMU or when running on different hardware.  This breaks
>>>   live migration and save/resume.
>>>
>>>   We also cannot break the command line interface.  If the last version
>>>   of QEMU supported -cpu POWER7_v2.1, then we must continue to support
>>>   that.
>>
>> 1a) How should -cpu 0xDEADBEEF or -cpu DEADBEEF behave.
>>
>>    I expect it to error out as before
>>    rather than applying the same fuzz/mask that -cpu host might.
> 
> I actually think it'd make sense to apply the same fuzz/mask, don't you think?

I think "-cpu host" has the semantics of give-me-what-the-host-has. But
-cpu 0xDEADBEEF is asking for PVR DEADBEEF and having it silently return
a guest-visible DEADBEBE is going to be undesired.

We could of course report our closest match on stderr for the user to
decide.

Andreas

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