Re: [PATCH v7 19/19] KVM: ARM64: Add a new kvm ARM PMU device

[Shannon Zhao <zhaoshenglong@huawei.com>]

On 2015/12/16 17:04, Marc Zyngier wrote:
> On 16/12/15 08:06, Shannon Zhao wrote:
>> > Hi,
>> > 
>> > On 2015/12/16 15:31, Shannon Zhao wrote:
>>>>>>>>> >>>>>>>> But in this case, you're returning an error if it is *not* initialized.
>>>>>>>>> >>>>>>>> I understand that in that case you cannot return an interrupt number (-1
>>>>>>>>> >>>>>>>> would be weird), but returning -EBUSY feels even more weird.
>>>>>>>>> >>>>>>>>
>>>>>>>>> >>>>>>>> I'd settle for -ENOXIO, or something similar. Anyone having a better idea?
>>>>>>>>> >>>>>>>>
>>>>> >>>> ENXIO or ENODEV would be my choice too, and add that to the
>>>>> >>>> Documentation clearly describing when this error code is used.
>>>>> >>>>
>>>>> >>>> By the way, why do you loop over all VCPUS to set the same value when
>>>>> >>>> you can't do anything per VCPU anyway?  It seems to me it's either a
>>>>> >>>> per-VM property (that you can store on the VM data structure) or it's a
>>>>> >>>> true per-VCPU property?
>>> >> This is a per-VCPU property. PMU interrupt could be PPI or SPI. For PPI
>>> >> the interrupt numbers are same for each vcpu, while for SPI they are
>>> >> different, so it needs to set them separately. I planned to support both
>>> >> PPI and SPI. I think I should add support for SPI at this moment and let
>>> >> users (QEMU) to set these interrupts for each one.
>> > 
>> > How about below vPMU Documentation?
>> > 
>> > ARM Virtual Performance Monitor Unit (vPMU)
>> > ===========================================
>> > 
>> > Device types supported:
>> >   KVM_DEV_TYPE_ARM_PMU_V3         ARM Performance Monitor Unit v3
>> > 
>> > Instantiate one PMU instance for per VCPU through this API.
>> > 
>> > Groups:
>> >   KVM_DEV_ARM_PMU_GRP_IRQ
>> >   Attributes:
>> >     The attr field of kvm_device_attr encodes two values:
>> >     bits:     | 63 .... 32 | 31 .... 0 |
>> >     values:   | vcpu_index |  irq_num  |
>> >     The irq_num describes the PMU overflow interrupt number for the
>> > specified
>> >     vcpu_index vcpu. This interrupt could be a PPI or SPI, but for one
>> > VM the
>> >     interrupt type must be same for each vcpu.
>> > 
>> >   Errors:
>> >     -ENXIO: Getting or setting this attribute is not yet supported
>> >     -ENODEV: Getting the PMU overflow interrupt number while it's not set
>> >     -EBUSY: The PMU overflow interrupt is already set
>> >     -EINVAL: Invalid vcpu_index or irq_num supplied
>> > 
>> > 
> Let's add at least one comment that forbids two vcpus from getting the
> same SPI. This is too common a mistake that we see in actual SoCs, and I
> don't want to see it replicated in VMs...

Ok, will add.

Thanks,
-- 
Shannon