| Message ID | 20211009021236.4122790-37-seanjc@google.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | KVM: Halt-polling and x86 APICv overhaul | expand |
On Fri, 2021-10-08 at 19:12 -0700, Sean Christopherson wrote: > 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> > --- > arch/x86/kvm/svm/avic.c | 15 +++++++++------ > arch/x86/kvm/svm/svm.h | 11 ----------- > 2 files changed, 9 insertions(+), 17 deletions(-) > > diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c > index cbf02e7e20d0..b43b05610ade 100644 > --- a/arch/x86/kvm/svm/avic.c > +++ b/arch/x86/kvm/svm/avic.c > @@ -295,13 +295,16 @@ static void avic_kick_target_vcpus(struct kvm *kvm, struct kvm_lapic *source, > struct kvm_vcpu *vcpu; > int 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); > } > } > diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h > index 0d7bbe548ac3..7f5b01bbee29 100644 > --- a/arch/x86/kvm/svm/svm.h > +++ b/arch/x86/kvm/svm/svm.h > @@ -509,17 +509,6 @@ extern struct kvm_x86_nested_ops svm_nested_ops; > > #define VMCB_AVIC_APIC_BAR_MASK 0xFFFFFFFFFF000ULL > > -static inline bool (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); I guess this makes sense to do, to get rid of the avic_vcpu_is_running. As you explained in previous patch, waking up a live task isn't that expensive, so let it be. Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com> Best regards, Maxim Levitsky
diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c index cbf02e7e20d0..b43b05610ade 100644 --- a/arch/x86/kvm/svm/avic.c +++ b/arch/x86/kvm/svm/avic.c @@ -295,13 +295,16 @@ static void avic_kick_target_vcpus(struct kvm *kvm, struct kvm_lapic *source, struct kvm_vcpu *vcpu; int 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); } } diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h index 0d7bbe548ac3..7f5b01bbee29 100644 --- a/arch/x86/kvm/svm/svm.h +++ b/arch/x86/kvm/svm/svm.h @@ -509,17 +509,6 @@ 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);
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> --- arch/x86/kvm/svm/avic.c | 15 +++++++++------ arch/x86/kvm/svm/svm.h | 11 ----------- 2 files changed, 9 insertions(+), 17 deletions(-)