Re: [RFC] KVM / QEMU: Introduce Interface for Querying APICv Info

[Chao Gao <chao.gao@intel.com>]

On Fri, May 20, 2022 at 10:30:40AM +0700, Suthikulpanit, Suravee wrote:
>Hi All,
>
>Currently, we don't have a good way to check whether APICV is active on a VM.
>Normally, For AMD SVM AVIC, users either have to check for trace point, or using
>"perf kvm stat live" to catch AVIC-related #VMEXIT.
>
>For KVM, I would like to propose introducing a new IOCTL interface (i.e. KVM_GET_APICV_INFO),
>where user-space tools (e.g. QEMU monitor) can query run-time information of APICv for VM and vCPUs
>such as APICv inhibit reason flags.
>
>For QEMU, we can leverage the "info lapic" command, and append the APICV information after
>all LAPIC register information:
>
>For example:
>
>----- Begin Snippet -----
>(qemu) info lapic 0
>dumping local APIC state for CPU 0
>
>LVT0     0x00010700 active-hi edge  masked                      ExtINT (vec 0)
>LVT1     0x00000400 active-hi edge                              NMI
>LVTPC    0x00010000 active-hi edge  masked                      Fixed  (vec 0)
>LVTERR   0x000000fe active-hi edge                              Fixed  (vec 254)
>LVTTHMR  0x00010000 active-hi edge  masked                      Fixed  (vec 0)
>LVTT     0x000400ee active-hi edge                 tsc-deadline Fixed  (vec 238)
>Timer    DCR=0x0 (divide by 2) initial_count = 0 current_count = 0
>SPIV     0x000001ff APIC enabled, focus=off, spurious vec 255
>ICR      0x000000fd physical edge de-assert no-shorthand
>ICR2     0x00000005 cpu 5 (X2APIC ID)
>ESR      0x00000000
>ISR      (none)
>IRR      (none)
>
>APR 0x00 TPR 0x00 DFR 0x0f LDR 0x00PPR 0x00
>
>APICV   vm inhibit: 0x10 <-- HERE
>APICV vcpu inhibit: 0 <-- HERE
>
>------ End Snippet ------
>
>Otherwise, we can have APICv-specific info command (e.g. info apicv).

I think this information can be added to kvm per-vm/vcpu debugfs. Then no
qemu change is needed.