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

[Marc Zyngier <marc.zyngier@arm.com>]

On 17/12/15 08:41, Shannon Zhao wrote:
> 
> 
> On 2015/12/17 16:33, Marc Zyngier wrote:
>> On Thu, 17 Dec 2015 15:22:50 +0800
>> Shannon Zhao <zhaoshenglong@huawei.com> wrote:
>>
>>>>
>>>>
>>>> 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 |
>> Using the .addr field for something that is clearly not an address is
>> rather odd. Is there any prior usage of that field for something that
>> is not an address?
> 
> I see this usage in vgic_attr_regs_access(). But if you prefer previous
> one, I'll use that.

Ah, you're using the .addr field to point to a userspace value, not to
carry the value itself! That'd be fine by me (even if I still prefer the
original one), but I'd like others to chime in (I'm quite bad at
defining userspace stuff...).

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...