Commit 187c8833 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: x86: Use rw_semaphore for APICv lock to allow vCPU parallelism 



Use a rw_semaphore instead of a mutex to coordinate APICv updates so that
vCPUs responding to requests can take the lock for read and run in
parallel.  Using a mutex forces serialization of vCPUs even though
kvm_vcpu_update_apicv() only touches data local to that vCPU or is
protected by a different lock, e.g. SVM's ir_list_lock.

Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20211022004927.1448382-5-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent ee49a893

arch/x86/include/asm/kvm_host.h

+1 −1
Original line number Diff line number Diff line
@@ -1071,7 +1071,7 @@ struct kvm_arch { 
	atomic_t apic_map_dirty;



	/* Protects apic_access_memslot_enabled and apicv_inhibit_reasons */

	struct mutex apicv_update_lock;

	struct rw_semaphore apicv_update_lock;



	bool apic_access_memslot_enabled;

	unsigned long apicv_inhibit_reasons;

arch/x86/kvm/hyperv.c

+2 −2
Original line number Diff line number Diff line
@@ -112,7 +112,7 @@ static void synic_update_vector(struct kvm_vcpu_hv_synic *synic, 
	if (!!auto_eoi_old == !!auto_eoi_new)

		return;



	mutex_lock(&vcpu->kvm->arch.apicv_update_lock);

	down_write(&vcpu->kvm->arch.apicv_update_lock);



	if (auto_eoi_new)

		hv->synic_auto_eoi_used++;
@@ -123,7 +123,7 @@ static void synic_update_vector(struct kvm_vcpu_hv_synic *synic, 
				   !hv->synic_auto_eoi_used,

				   APICV_INHIBIT_REASON_HYPERV);



	mutex_unlock(&vcpu->kvm->arch.apicv_update_lock);

	up_write(&vcpu->kvm->arch.apicv_update_lock);

}



static int synic_set_sint(struct kvm_vcpu_hv_synic *synic, int sint,

arch/x86/kvm/x86.c

+7 −5
Original line number Diff line number Diff line
@@ -8778,7 +8778,7 @@ EXPORT_SYMBOL_GPL(kvm_apicv_activated); 


static void kvm_apicv_init(struct kvm *kvm)

{

	mutex_init(&kvm->arch.apicv_update_lock);

	init_rwsem(&kvm->arch.apicv_update_lock);



	if (enable_apicv)

		clear_bit(APICV_INHIBIT_REASON_DISABLE,
@@ -9440,7 +9440,7 @@ void kvm_vcpu_update_apicv(struct kvm_vcpu *vcpu) 
	if (!lapic_in_kernel(vcpu))

		return;



	mutex_lock(&vcpu->kvm->arch.apicv_update_lock);

	down_read(&vcpu->kvm->arch.apicv_update_lock);



	activate = kvm_apicv_activated(vcpu->kvm);

	if (vcpu->arch.apicv_active == activate)
@@ -9460,7 +9460,7 @@ void kvm_vcpu_update_apicv(struct kvm_vcpu *vcpu) 
		kvm_make_request(KVM_REQ_EVENT, vcpu);



out:

	mutex_unlock(&vcpu->kvm->arch.apicv_update_lock);

	up_read(&vcpu->kvm->arch.apicv_update_lock);

}

EXPORT_SYMBOL_GPL(kvm_vcpu_update_apicv);
@@ -9468,6 +9468,8 @@ void __kvm_request_apicv_update(struct kvm *kvm, bool activate, ulong bit) 
{

	unsigned long old, new;



	lockdep_assert_held_write(&kvm->arch.apicv_update_lock);



	if (!kvm_x86_ops.check_apicv_inhibit_reasons ||

	    !static_call(kvm_x86_check_apicv_inhibit_reasons)(bit))

		return;
@@ -9506,9 +9508,9 @@ EXPORT_SYMBOL_GPL(__kvm_request_apicv_update); 


void kvm_request_apicv_update(struct kvm *kvm, bool activate, ulong bit)

{

	mutex_lock(&kvm->arch.apicv_update_lock);

	down_write(&kvm->arch.apicv_update_lock);

	__kvm_request_apicv_update(kvm, activate, bit);

	mutex_unlock(&kvm->arch.apicv_update_lock);

	up_write(&kvm->arch.apicv_update_lock);

}

EXPORT_SYMBOL_GPL(kvm_request_apicv_update);