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

From: Alexander Graf
Subject: Re: [Qemu-ppc] [Qemu-devel] [RFC PATCH] powerpc: add PVR mask support
Date: Thu, 15 Aug 2013 17:58:22 +0200

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 :).


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