| Message ID | 1643111979-36447-1-git-send-email-wanpengli@tencent.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [RESEND,v2] KVM: VMX: Dont' send posted IRQ if vCPU == this vCPU and vCPU is IN_GUEST_MODE | expand |
On 1/25/22 12:59, Wanpeng Li wrote: > From: Wanpeng Li <wanpengli@tencent.com> > > When delivering a virtual interrupt, don't actually send a posted interrupt > if the target vCPU is also the currently running vCPU and is IN_GUEST_MODE, > in which case the interrupt is being sent from a VM-Exit fastpath and the > core run loop in vcpu_enter_guest() will manually move the interrupt from > the PIR to vmcs.GUEST_RVI. IRQs are disabled while IN_GUEST_MODE, thus > there's no possibility of the virtual interrupt being sent from anything > other than KVM, i.e. KVM won't suppress a wake event from an IRQ handler > (see commit fdba608f15e2, "KVM: VMX: Wake vCPU when delivering posted IRQ > even if vCPU == this vCPU"). > > Eliding the posted interrupt restores the performance provided by the > combination of commits 379a3c8ee444 ("KVM: VMX: Optimize posted-interrupt > delivery for timer fastpath") and 26efe2fd92e5 ("KVM: VMX: Handle > preemption timer fastpath"). > > Thanks Sean for better comments. > > Suggested-by: Chao Gao <chao.gao@intel.com> > Reviewed-by: Sean Christopherson <seanjc@google.com> > Signed-off-by: Wanpeng Li <wanpengli@tencent.com> > --- > arch/x86/kvm/vmx/vmx.c | 40 +++++++++++++++++++++------------------- > 1 file changed, 21 insertions(+), 19 deletions(-) > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index fe06b02994e6..e06377c9a4cf 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -3908,31 +3908,33 @@ static inline void kvm_vcpu_trigger_posted_interrupt(struct kvm_vcpu *vcpu, > #ifdef CONFIG_SMP > if (vcpu->mode == IN_GUEST_MODE) { > /* > - * The vector of interrupt to be delivered to vcpu had > - * been set in PIR before this function. > + * The vector of the virtual has already been set in the PIR. > + * Send a notification event to deliver the virtual interrupt > + * unless the vCPU is the currently running vCPU, i.e. the > + * event is being sent from a fastpath VM-Exit handler, in > + * which case the PIR will be synced to the vIRR before > + * re-entering the guest. > * > - * Following cases will be reached in this block, and > - * we always send a notification event in all cases as > - * explained below. > + * When the target is not the running vCPU, the following > + * possibilities emerge: > * > - * Case 1: vcpu keeps in non-root mode. Sending a > - * notification event posts the interrupt to vcpu. > + * Case 1: vCPU stays in non-root mode. Sending a notification > + * event posts the interrupt to the vCPU. > * > - * Case 2: vcpu exits to root mode and is still > - * runnable. PIR will be synced to vIRR before the > - * next vcpu entry. Sending a notification event in > - * this case has no effect, as vcpu is not in root > - * mode. > + * Case 2: vCPU exits to root mode and is still runnable. The > + * PIR will be synced to the vIRR before re-entering the guest. > + * Sending a notification event is ok as the host IRQ handler > + * will ignore the spurious event. > * > - * Case 3: vcpu exits to root mode and is blocked. > - * vcpu_block() has already synced PIR to vIRR and > - * never blocks vcpu if vIRR is not cleared. Therefore, > - * a blocked vcpu here does not wait for any requested > - * interrupts in PIR, and sending a notification event > - * which has no effect is safe here. > + * Case 3: vCPU exits to root mode and is blocked. vcpu_block() > + * has already synced PIR to vIRR and never blocks the vCPU if > + * the vIRR is not empty. Therefore, a blocked vCPU here does > + * not wait for any requested interrupts in PIR, and sending a > + * notification event also results in a benign, spurious event. > */ > > - apic->send_IPI_mask(get_cpu_mask(vcpu->cpu), pi_vec); > + if (vcpu != kvm_get_running_vcpu()) > + apic->send_IPI_mask(get_cpu_mask(vcpu->cpu), pi_vec); > return; > } > #endif Queued, thanks. Paolo
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index fe06b02994e6..e06377c9a4cf 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -3908,31 +3908,33 @@ static inline void kvm_vcpu_trigger_posted_interrupt(struct kvm_vcpu *vcpu, #ifdef CONFIG_SMP if (vcpu->mode == IN_GUEST_MODE) { /* - * The vector of interrupt to be delivered to vcpu had - * been set in PIR before this function. + * The vector of the virtual has already been set in the PIR. + * Send a notification event to deliver the virtual interrupt + * unless the vCPU is the currently running vCPU, i.e. the + * event is being sent from a fastpath VM-Exit handler, in + * which case the PIR will be synced to the vIRR before + * re-entering the guest. * - * Following cases will be reached in this block, and - * we always send a notification event in all cases as - * explained below. + * When the target is not the running vCPU, the following + * possibilities emerge: * - * Case 1: vcpu keeps in non-root mode. Sending a - * notification event posts the interrupt to vcpu. + * Case 1: vCPU stays in non-root mode. Sending a notification + * event posts the interrupt to the vCPU. * - * Case 2: vcpu exits to root mode and is still - * runnable. PIR will be synced to vIRR before the - * next vcpu entry. Sending a notification event in - * this case has no effect, as vcpu is not in root - * mode. + * Case 2: vCPU exits to root mode and is still runnable. The + * PIR will be synced to the vIRR before re-entering the guest. + * Sending a notification event is ok as the host IRQ handler + * will ignore the spurious event. * - * Case 3: vcpu exits to root mode and is blocked. - * vcpu_block() has already synced PIR to vIRR and - * never blocks vcpu if vIRR is not cleared. Therefore, - * a blocked vcpu here does not wait for any requested - * interrupts in PIR, and sending a notification event - * which has no effect is safe here. + * Case 3: vCPU exits to root mode and is blocked. vcpu_block() + * has already synced PIR to vIRR and never blocks the vCPU if + * the vIRR is not empty. Therefore, a blocked vCPU here does + * not wait for any requested interrupts in PIR, and sending a + * notification event also results in a benign, spurious event. */ - apic->send_IPI_mask(get_cpu_mask(vcpu->cpu), pi_vec); + if (vcpu != kvm_get_running_vcpu()) + apic->send_IPI_mask(get_cpu_mask(vcpu->cpu), pi_vec); return; } #endif