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.
That would let us implement our own fuzz logic in kvm.c,
operating on a GSList of ObjectClasses to handle multiple matches.
Regards,
Andreas
>
> If there's a good reason to break either of these, that's fine but
> that justification needs be up front in the patch commit message.
>
> 2) The only "-cpu" that makes sense is "-cpu host" for KVM on HV (or
> whatever ya'll call it). POWER does not have the ability to
> virtualize the hardware PVR value. There is a virtual PVR in the
> device tree but that's orthogonal to what we think of as the VCPU (it
> essentially means IIUC that the cpu is compatible with that PVR).
>
> We should explicitly disallow any -cpu value when KVM on HV is
> enabled other than host.
>
> The implementation of "-cpu host" is also goofy on PPC. -cpu host
> does a match on existing CPU models meaning that we have to define a
> CPU model for any possible CPU we run on. This would require having
> every possible CPU model implemented in QEMU which is silly.
> Instead, we should have a passthrough CPU model for use with "-cpu
> host" which is essentially what Alexey's patch turns -cpu POWER7
> into.
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