Re: [RFC PATCH v3 01/19] KVM: x86: document AVIC/APICv inhibit reasons

Maxim Levitsky
2022-05-18T17:14:26Z

On Wed, 2022-05-18 at 15:56 +0000, Sean Christopherson wrote:
> On Wed, Apr 27, 2022, Maxim Levitsky wrote:
> > These days there are too many AVIC/APICv inhibit
> > reasons, and it doesn't hurt to have some documentation
> > for them.
>
> Please wrap at ~75 chars.
>
> > Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> > ---
> > arch/x86/include/asm/kvm_host.h | 15 +++++++++++++++
> > 1 file changed, 15 insertions(+)
> >
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index f164c6c1514a4..63eae00625bda 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -1046,14 +1046,29 @@ struct kvm_x86_msr_filter {
> > };
> >
> > enum kvm_apicv_inhibit {
> > + /* APICv/AVIC is disabled by module param and/or not supported in hardware */
>
> Rather than tag every one as APICv vs. AVIC, what about reorganizing the enums so
> that the common vs. AVIC flags are bundled together? And then the redundant info
> in the comments about "XYZ is inhibited" can go away too, i.e. the individual
> comments can focus on explaining what triggers the inhibit (and for some, why that
> action is incompatible with APIC virtualization).

Very good idea, will do!

Best regards,
Maxim Levitsky

>
> E.g.
> /***************************************************************/
> /* INHIBITs are relevant to both Intel's APICv and AMD's AVIC. */
> /***************************************************************/
>
> /* APIC/AVIC is unsupported and/or disabled via module param. */
> APICV_INHIBIT_REASON_DISABLE,
>
> /* The local APIC is not in-kernel. See KVM_CREATE_IRQCHIP. */
> APICV_INHIBIT_REASON_ABSENT,
>
> /*
> * At least one IRQ vector is configured for HyperV's AutoEOI, which
> * requires manually injecting the IRQ to do EOI on behalf of the guest.
> */
> APICV_INHIBIT_REASON_HYPERV,
>
>
> /**********************************************/
> /* INHIBITs relevant only to AMD's AVIC. */
> /**********************************************/
>
> > APICV_INHIBIT_REASON_DISABLE,
> > + /* APICv/AVIC is inhibited because AutoEOI feature is being used by a HyperV guest*/
> > APICV_INHIBIT_REASON_HYPERV,
> > + /* AVIC is inhibited on a CPU because it runs a nested guest */
> > APICV_INHIBIT_REASON_NESTED,
> > + /* AVIC is inhibited due to wait for an irq window (AVIC doesn't support this) */
> > APICV_INHIBIT_REASON_IRQWIN,
> > + /*
> > + * AVIC is inhibited because i8254 're-inject' mode is used
> > + * which needs EOI intercept which AVIC doesn't support
> > + */
> > APICV_INHIBIT_REASON_PIT_REINJ,
> > + /* AVIC is inhibited because the guest has x2apic in its CPUID*/
> > APICV_INHIBIT_REASON_X2APIC,
> > + /* AVIC/APICv is inhibited because KVM_GUESTDBG_BLOCKIRQ was enabled */
> > APICV_INHIBIT_REASON_BLOCKIRQ,
> > + /*
> > + * AVIC/APICv is inhibited because the guest didn't yet
>
> s/guest/userspace
>
> > + * enable kernel/split irqchip
> > + */
> > APICV_INHIBIT_REASON_ABSENT,
> > + /* AVIC is disabled because SEV doesn't support it */
> > APICV_INHIBIT_REASON_SEV,
> > };
> >
> > --
> > 2.26.3
> >