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

[Shannon Zhao <zhaoshenglong@huawei.com>]

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.

-- 
Shannon