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

[Alexander Graf]

On 15.08.2013, at 17:48, Andreas Färber wrote:

> 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.

-cpu host on 0xDEADBEEF should give us a 0xDEADBEEF cpu. -cpu 0xDEADBEEF should 
give us a 0xDEADBEEF cpu :).


Alex