On Thu, Dec 08, 2022, Maxim Levitsky wrote:
> On Sat, 2022-10-01 at 00:59 +0000, Sean Christopherson wrote:
> > Inhibit APICv/AVIC if the optimized physical map is disabled so that KVM
> > KVM provides consistent APIC behavior if xAPIC IDs are aliased due to
> > vcpu_id being truncated and the x2APIC hotplug hack isn't enabled. If
> > the hotplug hack is disabled, events that are emulated by KVM will follow
> > architectural behavior (all matching vCPUs receive events, even if the
> > "match" is due to truncation), whereas APICv and AVIC will deliver events
> > only to the first matching vCPU, i.e. the vCPU that matches without
> > truncation.
> >
> > Note, the "extra" inhibit is needed because KVM deliberately ignores
> > mismatches due to truncation when applying the APIC_ID_MODIFIED inhibit
> > so that large VMs (>255 vCPUs) can run with APICv/AVIC.
> >
> > Fixes: TDB
> Do you mean Trade & Development Bank of Mongolia ? ;-)
Heh, this fixes a patch/commit earlier in the series, hence the placeholder.
> > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> > ---
> > arch/x86/include/asm/kvm_host.h | 6 ++++++
> > arch/x86/kvm/lapic.c | 13 ++++++++++++-
> > arch/x86/kvm/svm/avic.c | 1 +
> > arch/x86/kvm/vmx/vmx.c | 1 +
> > 4 files changed, 20 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index ac28bbfbf0e3..171e38b94c89 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -1104,6 +1104,12 @@ enum kvm_apicv_inhibit {
> > */
> > APICV_INHIBIT_REASON_BLOCKIRQ,
> >
> > + /*
> > + * APICv is disabled because not all vCPUs have a 1:1 mapping between
> > + * APIC ID and vCPU, _and_ KVM is not applying its x2APIC hotplug hack.
> > + */
> > + APICV_INHIBIT_REASON_PHYSICAL_ID_ALIASED,
> > +
> > /*
> > * For simplicity, the APIC acceleration is inhibited
> > * first time either APIC ID or APIC base are changed by the guest
> > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> > index 340c2d3e781b..f6f328d36ae2 100644
> > --- a/arch/x86/kvm/lapic.c
> > +++ b/arch/x86/kvm/lapic.c
> > @@ -381,6 +381,16 @@ void kvm_recalculate_apic_map(struct kvm *kvm)
> > cluster[ldr] = apic;
> > }
> > out:
> > + /*
> > + * The optimized map is effectively KVM's internal version of APICv,
> Nitpick: APICv/AVIC?
Hmm. I think my preference for common code that doesn't need to differentiate
between Intel and AMD (or AVIC vs. x2AVIC) is to use just APICv. "APICv" is a
mostly a KVM term, e.g. Intel uses "APIC-virtualization" as an umbrella term for
a massive pile of features, so I think bending the term to cover Intel+AMD is ok?
Typing APICv/AVIC everywhere will get tedious and creates its own flavor of
confusion, e.g. the inhibits all use APICV.
