Re: [PATCH v8 20/20] KVM: ARM64: Add a new kvm ARM PMU device

[Peter Maydell <peter.maydell@linaro.org>]

On 8 January 2016 at 03:06, Shannon Zhao <zhaoshenglong@huawei.com> wrote:
>
>
> On 2016/1/7 22:56, Peter Maydell wrote:
>>>>> +  Errors:
>>>>> >>> +    -ENXIO: Unsupported attribute group
>>>>> >>> +    -EBUSY: The PMU overflow interrupt is already set
>>>>> >>> +    -ENODEV: Getting the PMU overflow interrupt number while it's not set
>>>>> >>> +    -EINVAL: Invalid vcpu_index or PMU overflow interrupt number supplied
>>>> >>
>>>> >> What happens if you create a PMU but then never set the IRQ number?
>>>> >> Is there a default or does the VM refuse to run or something?
>>>> >>
>>> > If userspace doesn't specify the irq number, the guest will not receive
>>> > the PMU interrupt because we check if the irq is initialized when we
>>> > inject the interrupt. But guest could still use the vPMU if QEMU
>>> > generates a proper DTB or ACPI.
>> So is it a valid use case to create a PMU with the interrupt not wired
>> up to anything? (If it's never valid it would be nice to diagnose it
>> rather than just silently letting the guest run but not work right.)
> So how about adding a helper to check if the PMU is completely
> initialized and if not, return trap_raz_wi when guest access PMU registers?

That would still be letting the guest run and not work right.

If we have an "I have now completed config" ioctl like the GIC does,
then you could make that ioctl return an error if the config is not
valid.

thanks
-- PMM