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KVM: x86: Skip APICv update if APICv is disable at the module level 

Bail from the APICv update paths _before_ taking apicv_update_lock if
APICv is disabled at the module level.  kvm_request_apicv_update() in
particular is invoked from multiple paths that can be reached without
APICv being enabled, e.g. svm_enable_irq_window(), and taking the
rw_sem for write when APICv is disabled may introduce unnecessary
contention and stalls.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20211208015236.1616697-25-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2021-12-08 01:52:34 +00:00 committed by Paolo Bonzini
parent 7446cfebe8
commit f15756428d
2 changed files with 6 additions and 0 deletions
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3
arch/x86/kvm/hyperv.c
View File

@ -112,6 +112,9 @@ static void synic_update_vector(struct kvm_vcpu_hv_synic *synic,
if (!!auto_eoi_old == !!auto_eoi_new)
return;
if (!enable_apicv)
return;
down_write(&vcpu->kvm->arch.apicv_update_lock);
if (auto_eoi_new)

3
arch/x86/kvm/x86.c
View File

@ -9715,6 +9715,9 @@ void __kvm_request_apicv_update(struct kvm *kvm, bool activate, ulong bit)
void kvm_request_apicv_update(struct kvm *kvm, bool activate, ulong bit)
{
if (!enable_apicv)
return;
down_write(&kvm->arch.apicv_update_lock);
__kvm_request_apicv_update(kvm, activate, bit);
up_write(&kvm->arch.apicv_update_lock);