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 <mlevitsk@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20230106011306.85230-24-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 732421a0ad02413b6c05cc4d02cb6d1e61440ebb..5865bad08a23cdfc963da8a7a119d68a770b2507 100644 (file)
--- 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 e9f258de91bdfc0e66fa43f59b5ec8384d0bfd0e..297da684c25f09c0da3fa7bc73304b978e12b0b4 100644 (file)
--- 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 76da9f19272ece078aa1f010dc92f8c8d31f1ca4..d1ac19f053ce22384368f27fee7dba9e4ceded7f 100644 (file)
--- 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 8ed14fcfe87003bdd3074746489abd8607a51bf6..ef84d11a0fe4489e3daab5b57915fe4c73a81bc9 100644 (file)
--- 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);