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KVM: SVM: Skip AVIC and IRTE updates when loading blocking vCPU

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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>
This commit is contained in:
Sean Christopherson 2021-12-08 01:52:24 +00:00 committed by Paolo Bonzini
parent af52f5aa5c
commit 782f64558d
1 changed files with 18 additions and 14 deletions
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32
arch/x86/kvm/svm/avic.c
View file

@ -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);