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

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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: Sean Christopherson <seanjc@google.com>
Message-Id: <20211022004927.1448382-5-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson
2021-10-21 17:49:27 -07:00
committed by Paolo Bonzini
parent ee49a89329
commit 187c8833de
3 changed files with 10 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
arch/x86/include/asm/kvm_host.h
View File

@@ -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;

4
arch/x86/kvm/hyperv.c
View File

@@ -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,

12
arch/x86/kvm/x86.c
View File

@@ -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);