From 5063c41bebac8d18a83ac7b5d54782d73a9ab5f7 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Fri, 6 Jan 2023 01:12:56 +0000 Subject: [PATCH] KVM: x86: Inhibit APICv/AVIC if the optimized physical map is disabled 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. Reviewed-by: Maxim Levitsky Signed-off-by: Sean Christopherson Message-Id: <20230106011306.85230-24-seanjc@google.com> Signed-off-by: Paolo Bonzini --- 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 732421a0ad02..5865bad08a23 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1174,6 +1174,12 @@ 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 e9f258de91bd..297da684c25f 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -386,6 +386,16 @@ void kvm_recalculate_apic_map(struct kvm *kvm) cluster[ldr] = apic; } out: + /* + * The optimized map is effectively KVM's internal version of APICv, + * and all unwanted aliasing that results in disabling the optimized + * map also applies to APICv. + */ + if (!new) + kvm_set_apicv_inhibit(kvm, APICV_INHIBIT_REASON_PHYSICAL_ID_ALIASED); + else + kvm_clear_apicv_inhibit(kvm, APICV_INHIBIT_REASON_PHYSICAL_ID_ALIASED); + old = rcu_dereference_protected(kvm->arch.apic_map, lockdep_is_held(&kvm->arch.apic_map_lock)); rcu_assign_pointer(kvm->arch.apic_map, new); @@ -2158,7 +2168,8 @@ static void kvm_lapic_xapic_id_updated(struct kvm_lapic *apic) /* * Deliberately truncate the vCPU ID when detecting a modified APIC ID * to avoid false positives if the vCPU ID, i.e. x2APIC ID, is a 32-bit - * value. + * value. If the wrap/truncation results in unwanted aliasing, APICv + * will be inhibited as part of updating KVM's optimized APIC maps. */ if (kvm_xapic_id(apic) == (u8)apic->vcpu->vcpu_id) return; diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c index 76da9f19272e..d1ac19f053ce 100644 --- a/arch/x86/kvm/svm/avic.c +++ b/arch/x86/kvm/svm/avic.c @@ -965,6 +965,7 @@ bool avic_check_apicv_inhibit_reasons(enum kvm_apicv_inhibit reason) BIT(APICV_INHIBIT_REASON_PIT_REINJ) | BIT(APICV_INHIBIT_REASON_BLOCKIRQ) | BIT(APICV_INHIBIT_REASON_SEV) | + BIT(APICV_INHIBIT_REASON_PHYSICAL_ID_ALIASED) | BIT(APICV_INHIBIT_REASON_APIC_ID_MODIFIED) | BIT(APICV_INHIBIT_REASON_APIC_BASE_MODIFIED); diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 8ed14fcfe870..ef84d11a0fe4 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -8029,6 +8029,7 @@ static bool vmx_check_apicv_inhibit_reasons(enum kvm_apicv_inhibit reason) BIT(APICV_INHIBIT_REASON_ABSENT) | BIT(APICV_INHIBIT_REASON_HYPERV) | BIT(APICV_INHIBIT_REASON_BLOCKIRQ) | + BIT(APICV_INHIBIT_REASON_PHYSICAL_ID_ALIASED) | BIT(APICV_INHIBIT_REASON_APIC_ID_MODIFIED) | BIT(APICV_INHIBIT_REASON_APIC_BASE_MODIFIED);