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KVM: SVM: Don't bother checking for "running" AVIC when kicking for IPIs

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Drop the avic_vcpu_is_running() check when waking vCPUs in response to a
VM-Exit due to incomplete IPI delivery.  The check isn't wrong per se, but
it's not 100% accurate in the sense that it doesn't guarantee that the vCPU
was one of the vCPUs that didn't receive the IPI.

The check isn't required for correctness as blocking == !running in this
context.

From a performance perspective, waking a live task is not expensive as the
only moderately costly operation is a locked operation to temporarily
disable preemption.  And if that is indeed a performance issue,
kvm_vcpu_is_blocking() would be a better check than poking into the AVIC.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20211208015236.1616697-12-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2021-12-08 01:52:21 +00:00 committed by Paolo Bonzini
parent 31f251d4dd
commit 202470d536
2 changed files with 9 additions and 17 deletions
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15
arch/x86/kvm/svm/avic.c
View File

@ -295,13 +295,16 @@ static void avic_kick_target_vcpus(struct kvm *kvm, struct kvm_lapic *source,
struct kvm_vcpu *vcpu;
unsigned long i;
/*
* Wake any target vCPUs that are blocking, i.e. waiting for a wake
* event. There's no need to signal doorbells, as hardware has handled
* vCPUs that were in guest at the time of the IPI, and vCPUs that have
* since entered the guest will have processed pending IRQs at VMRUN.
*/
kvm_for_each_vcpu(i, vcpu, kvm) {
bool m = kvm_apic_match_dest(vcpu, source,
icrl & APIC_SHORT_MASK,
GET_APIC_DEST_FIELD(icrh),
icrl & APIC_DEST_MASK);
if (m && !avic_vcpu_is_running(vcpu))
if (kvm_apic_match_dest(vcpu, source, icrl & APIC_SHORT_MASK,
GET_APIC_DEST_FIELD(icrh),
icrl & APIC_DEST_MASK))
kvm_vcpu_wake_up(vcpu);
}
}

11
arch/x86/kvm/svm/svm.h
View File

@ -573,17 +573,6 @@ extern struct kvm_x86_nested_ops svm_nested_ops;
#define VMCB_AVIC_APIC_BAR_MASK 0xFFFFFFFFFF000ULL
static inline bool avic_vcpu_is_running(struct kvm_vcpu *vcpu)
{
struct vcpu_svm *svm = to_svm(vcpu);
u64 *entry = svm->avic_physical_id_cache;
if (!entry)
return false;
return (READ_ONCE(*entry) & AVIC_PHYSICAL_ID_ENTRY_IS_RUNNING_MASK);
}
int avic_ga_log_notifier(u32 ga_tag);
void avic_vm_destroy(struct kvm *kvm);
int avic_vm_init(struct kvm *kvm);