Re: [Qemu-devel] [Help] Windows2012 as Guest 64+cores on KVM Halts

[Paolo Bonzini <pbonzini@redhat.com>]

On 20/02/2017 12:54, Gonglei (Arei) wrote:
>>
>> On 20/02/2017 10:19, Gonglei (Arei) wrote:
>>> Hi Paolo,
>>>
>>>>
>>>>
>>>> On 16/02/2017 02:31, Gonglei (Arei) wrote:
>>>>> And the below patch works for me, I can support max 255 vcpus for
>> WS2012
>>>>> with hyper-v enlightenments.
>>>>>
>>>>> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
>>>>> index 27fd050..efe3cbc 100644
>>>>> --- a/target/i386/kvm.c
>>>>> +++ b/target/i386/kvm.c
>>>>> @@ -772,7 +772,7 @@ int kvm_arch_init_vcpu(CPUState *cs)
>>>>>
>>>>>          c = &cpuid_data.entries[cpuid_i++];
>>>>>          c->function = HYPERV_CPUID_IMPLEMENT_LIMITS;
>>>>> -        c->eax = 0x40;
>>>>> +        c->eax = -1;
>>>>>          c->ebx = 0x40;
>>>>>
>>>>>          kvm_base = KVM_CPUID_SIGNATURE_NEXT;
>>>>
>>>> This needs to depend on the machine type, but apart from that I think
>>>
>>> I don't know why. Because the negative effects for this change don't exist
>>> on current QEMU IIUC, and we don't have compatible problems for live
>> migration.
>>
>> CPUID should never change with the same machine type and command line.
>>
> OK, then how do we add compat code for the CPUID change? It's not a visible property.

You can add a new property, something like hv-cpuid-limits-eax.

Paolo