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

[Shannon Zhao <zhaoshenglong@huawei.com>]

On 2015/12/17 4:33, Christoffer Dall wrote:
> On Wed, Dec 16, 2015 at 04:06:49PM +0800, 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  |
BTW, I change this Attribute to below format and pass vcpu_index through
this Attribute while pass irq_num through kvm_device_attr.addr.
Is it fine?

    bits:     | 63 .... 32 | 31 ....  0 |
    values:   |  reserved  | vcpu_index |

>>     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.
> 
> some formatting snafus that I expect come from pasting the text in an
> e-mail client.
> 
>>
>>   Errors:
>>     -ENXIO: Getting or setting this attribute is not yet supported
> 
> 'not yet supported' as in something we'll implement later, or as in you
> need to call this other function before you can access this state?
> 
Since only when the group is not KVM_DEV_ARM_PMU_GRP_IRQ, it will return
-ENXIO. So what about this?

"-ENXIO: Unsupported attribute group"

Thanks,
-- 
Shannon