From 9b44423bf4c8570834679879a8d26928d9e962e2 Mon Sep 17 00:00:00 2001 From: Wanpeng Li Date: Tue, 25 Jan 2022 03:59:39 -0800 Subject: [PATCH] KVM: VMX: Dont' send posted IRQ if vCPU == this vCPU and vCPU is IN_GUEST_MODE 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 Reviewed-by: Sean Christopherson Signed-off-by: Wanpeng Li Message-Id: <1643111979-36447-1-git-send-email-wanpengli@tencent.com> Signed-off-by: Paolo Bonzini --- 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 cb54342..a40130e 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -3937,31 +3937,33 @@ 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 -- 2.7.4