Re: [Qemu-ppc] [PATCH v4 2/2] target/ppc: move POWER9 DD1 workaround to init_proc_POWER9()

[Thomas Huth]

On 05.07.2017 08:36, David Gibson wrote:
> On Tue, Jul 04, 2017 at 03:02:39PM +0200, Greg Kurz wrote:
>> On Tue, 4 Jul 2017 21:41:51 +1000
>> David Gibson <address@hidden> wrote:
>>
>>> On Tue, Jul 04, 2017 at 01:15:00PM +0200, Greg Kurz wrote:
>>>> On Tue,  4 Jul 2017 13:01:26 +0200
>>>> Laurent Vivier <address@hidden> wrote:
>>>>   
>>>>> Commit 5f3066d ("target/ppc: Allow workarounds for POWER9 DD1")
>>>>> disables compatibility mode for POWER9 DD1 to allow to
>>>>> boot on POWER9 DD1 host with KVM.
>>>>>
>>>>> As the workaround has been added in kvmppc_host_cpu_class_init(),
>>>>> it applies only on CPU created with "-cpu host".
>>>>> As we want to be able to use also "-cpu POWER9" on a POWER9 DD1
>>>>> host, this patch moves the workaround from kvmppc_host_cpu_class_init()
>>>>> to init_proc_POWER9().
>>>>>   
>>>>
>>>> As with ppc_cpu_initfn() in your previous version, init_proc_POWER9() is
>>>> called for every CPU instance.. ie, all CPU will adjust the @pcr_supported
>>>> class attribute...  
>>>
>>> Ah.. yeah.. I didn't notice that before.  That's definitely not right.
>>>
>>>> What about moving the workaround to ppc_POWER9_cpu_family_class_init()
>>>> instead ? This would just require to expose mfpvr() in some header.  
>>>
>>> Yeah, as someone else pointed out using the host PVR is also
>>> definitely not right (unless you're in a function specifically
>>> connected to the host cpu class).
>>>
>>
>> I agree but the root issue is that we accept to pass -cpu POWER9 instead of
>> -cpu host with -enable-kvm. And the host cpu class isn't involved in this
>> case.
> 
> Well.. it sort of is.  I believe the way we make this work (since
> Thomas' cleanup) is that when KVM is active, we alter the alias for
> the host cpu's family to point to the host cpu class, instead of
> whatever specific version it usually points to.

Right, it's the code at the and of the kvm_ppc_register_host_cpu_type()
function. Maybe that function could also be a good spot to move the DD1
workaround into (just a quick idea, I haven't checked whether it's
feasible)?

 Thomas

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