Re: [Qemu-devel] [RFC PATCH V2 3/6] target-arm: Enable KVM_ARM_VCPU_PSCI_0_2 feature when possible

[Pranavkumar Sawargaonkar]

Hi Peter,

On 1 April 2014 17:46, Peter Maydell <address@hidden> wrote:
> On 1 April 2014 12:53, Pranavkumar Sawargaonkar <address@hidden> wrote:
>> Latest linux kernel supports in-kernel emulation of PSCI v0.2 but
>> to enable it we need to select KVM_ARM_VCPU_PSCI_0_2 feature using
>> KVM_ARM_VCPU_INIT ioctl.
>>
>> Also, we can use KVM_ARM_VCPU_PSCI_0_2 feature for VCPU only when
>> linux kernel has KVM_CAP_ARM_PSCI_0_2 capability.
>>
>> This patch updates kvm_arch_init_vcpu() to enable KVM_ARM_VCPU_PSCI_0_2
>> feature for VCPU when KVM ARM/ARM64 has KVM_CAP_ARM_PSCI_0_2 capability.
>>
>> Signed-off-by: Pranavkumar Sawargaonkar <address@hidden>
>> Signed-off-by: Anup Patel <address@hidden>
>> ---
>>  target-arm/kvm32.c |    5 ++++-
>>  target-arm/kvm64.c |    5 ++++-
>>  2 files changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/target-arm/kvm32.c b/target-arm/kvm32.c
>> index a4fde07..afeff01 100644
>> --- a/target-arm/kvm32.c
>> +++ b/target-arm/kvm32.c
>> @@ -181,7 +181,10 @@ int kvm_arch_init_vcpu(CPUState *cs)
>>      init.target = cpu->kvm_target;
>>      memset(init.features, 0, sizeof(init.features));
>>      if (cpu->start_powered_off) {
>> -        init.features[0] = 1 << KVM_ARM_VCPU_POWER_OFF;
>> +        init.features[0] |= 1 << KVM_ARM_VCPU_POWER_OFF;
>> +    }
>> +    if (kvm_check_extension(cs->kvm_state, KVM_CAP_ARM_PSCI_0_2)) {
>> +        init.features[0] |= 1 << KVM_ARM_VCPU_PSCI_0_2;
>>      }
>
> I vaguely remember mentioning migration incompatibilities
> last time round. You can't do this because this means that
> a QEMU running on a non-0.2-aware kernel won't be able to
> migrate its VM to a QEMU running on a 0.2-aware kernel.
> PSCI version is probably going to need to be a CPU property;
> needs more thought.
>

Yes you had mentioned about this issue in v1.
During V1 of this patch-set Christoffer mentioned that he will address
this issue in migration for ARMv8.
But till that time can we go with this current approach ? (May be I
can add a comment about this)

> thanks
> -- PMM

Thanks,
Pranav