Re: [PATCH v2 04/15] kvm: x86: Add per-VM APICv state debugfs

[Suthikulpanit, Suravee]

Alex,

On 8/27/19 3:20 AM, Alexander Graf wrote:
> 
> 
> On 26.08.19 21:41, Suthikulpanit, Suravee wrote:
>> Alex,
>>
>> On 8/19/2019 4:57 AM, Alexander Graf wrote:
>>>
>>>
>>> On 15.08.19 18:25, Suthikulpanit, Suravee wrote:
>>>> Currently, there is no way to tell whether APICv is active
>>>> on a particular VM. This often cause confusion since APICv
>>>> can be deactivated at runtime.
>>>>
>>>> Introduce a debugfs entry to report APICv state of a VM.
>>>> This creates a read-only file:
>>>>
>>>> ÂÂÂÂ /sys/kernel/debug/kvm/70860-14/apicv-state
>>>>
>>>> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
>>>
>>> Shouldn't this first and foremost be a VM ioctl so that user space 
>>> can inquire its own state?
>>>
>>>
>>> Alex
>>
>> I introduce this mainly for debugging similar to how KVM is currently 
>> provides
>> some per-VCPU information:
>>
>> ÂÂÂÂÂ /sys/kernel/debug/kvm/15957-14/vcpu0/
>> ÂÂÂÂÂÂÂÂÂ lapic_timer_advance_ns
>> ÂÂÂÂÂÂÂÂÂ tsc-offset
>> ÂÂÂÂÂÂÂÂÂ tsc-scaling-ratio
>> ÂÂÂÂÂÂÂÂÂ tsc-scaling-ratio-frac-bits
>>
>> I'm not sure if this needs to be VM ioctl at this point. If this 
>> information is
>> useful for user-space tool to inquire via ioctl, we can also provide it.
> 
> I'm mostly thinking of something like "info apic" in QEMU which to me 
> seems like the natural place for APIC information exposure to a user.

I could not find QEMU "info apic". I assume you meant "info lapic", 
which provides information specific to each local APIC (i.e. per-vcpu).

> The problem with debugfs is that it's not accessible to the user that 
> created the VM, but only root, right?

Hm, you are right. I'll also look into also adding ioctl interface then.

Thanks,
Suravee