Re: [Question] Regarding PMU initialization within the QEMU for ARM VCPUs

[Auger Eric <eric.auger@redhat.com>]

Hi Drew,
On 6/3/20 12:21 PM, Andrew Jones wrote:
> On Wed, Jun 03, 2020 at 11:59:23AM +0200, Auger Eric wrote:
>> Hi Drew,
>>
>> On 6/3/20 11:37 AM, Andrew Jones wrote:
>>> On Mon, Jun 01, 2020 at 03:04:33PM +0000, Salil Mehta wrote:
>>>> Hello,
>>>> I could see below within function fdt_add_pmu_nodes() part of
>>>> hw/arm/virt.c during virt machine initialization time:
>>>>
>>>> Observation:
>>>> In below function, support of PMU feature is being checked for
>>>> each vcpu and if the PMU is found part of the features then PMU
>>>> is initialized with in the host/KVM. But if there is even one
>>>> vcpu which is found to not support the PMU then loop is exited
>>>> and PMU is not initialized for the rest of the vcpus as well.
>>>>
>>>> Questions:
>>>> Q1. Not sure what is the logic of the premature exit and not
>>>>     continuing with further checks and initialization of other
>>>>     VCPU PMUs?
>>>
>>> KVM requires all VCPUs to have a PMU if one does.
>>
>> I fail to find where this is enforced? Do you know the place?
> 
> kvm_vcpu_set_target(), called from KVM_ARM_VCPU_INIT. It ensures
> all VCPUs have identical features selected. The PMU requires a
> VCPU feature (KVM_ARM_VCPU_PMU_V3) to be set.
OK thanks!

Eric
> 
> Thanks,
> drew
>