KVM: SVM: Skip AVIC and IRTE updates when loading blocking vCPU
Don't bother updating the Physical APIC table or IRTE when loading a vCPU
that is blocking, i.e. won't be marked IsRun{ning}=1, as the pCPU is
queried if and only if IsRunning is '1'. If the vCPU was migrated, the
new pCPU will be picked up when avic_vcpu_load() is called by
svm_vcpu_unblocking().
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211208015236.1616697-15-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 3688133..b7353e1 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -975,7 +975,6 @@ void avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
{
u64 entry;
/* ID = 0xff (broadcast), ID > 0xff (reserved) */
- bool is_blocking = kvm_vcpu_is_blocking(vcpu);
int h_physical_id = kvm_cpu_get_apicid(cpu);
struct vcpu_svm *svm = to_svm(vcpu);
@@ -986,24 +985,25 @@ void avic_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
if (WARN_ON(h_physical_id > AVIC_PHYSICAL_ID_ENTRY_HOST_PHYSICAL_ID_MASK))
return;
+ /*
+ * No need to update anything if the vCPU is blocking, i.e. if the vCPU
+ * is being scheduled in after being preempted. The CPU entries in the
+ * Physical APIC table and IRTE are consumed iff IsRun{ning} is '1'.
+ * If the vCPU was migrated, its new CPU value will be stuffed when the
+ * vCPU unblocks.
+ */
+ if (kvm_vcpu_is_blocking(vcpu))
+ return;
+
entry = READ_ONCE(*(svm->avic_physical_id_cache));
WARN_ON(entry & AVIC_PHYSICAL_ID_ENTRY_IS_RUNNING_MASK);
entry &= ~AVIC_PHYSICAL_ID_ENTRY_HOST_PHYSICAL_ID_MASK;
entry |= (h_physical_id & AVIC_PHYSICAL_ID_ENTRY_HOST_PHYSICAL_ID_MASK);
-
- entry &= ~AVIC_PHYSICAL_ID_ENTRY_IS_RUNNING_MASK;
-
- /*
- * Don't mark the vCPU as running if its blocking, i.e. if the vCPU is
- * preempted after svm_vcpu_blocking() but before KVM voluntarily
- * schedules out the vCPU.
- */
- if (!is_blocking)
- entry |= AVIC_PHYSICAL_ID_ENTRY_IS_RUNNING_MASK;
+ entry |= AVIC_PHYSICAL_ID_ENTRY_IS_RUNNING_MASK;
WRITE_ONCE(*(svm->avic_physical_id_cache), entry);
- avic_update_iommu_vcpu_affinity(vcpu, h_physical_id, !is_blocking);
+ avic_update_iommu_vcpu_affinity(vcpu, h_physical_id, true);
}
void avic_vcpu_put(struct kvm_vcpu *vcpu)
@@ -1012,8 +1012,12 @@ void avic_vcpu_put(struct kvm_vcpu *vcpu)
struct vcpu_svm *svm = to_svm(vcpu);
entry = READ_ONCE(*(svm->avic_physical_id_cache));
- if (entry & AVIC_PHYSICAL_ID_ENTRY_IS_RUNNING_MASK)
- avic_update_iommu_vcpu_affinity(vcpu, -1, 0);
+
+ /* Nothing to do if IsRunning == '0' due to vCPU blocking. */
+ if (!(entry & AVIC_PHYSICAL_ID_ENTRY_IS_RUNNING_MASK))
+ return;
+
+ avic_update_iommu_vcpu_affinity(vcpu, -1, 0);
entry &= ~AVIC_PHYSICAL_ID_ENTRY_IS_RUNNING_MASK;
WRITE_ONCE(*(svm->avic_physical_id_cache), entry);