From 29802380b6793eabcac648e1c097c7bd6333f3d4 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Fri, 8 Oct 2021 19:12:17 -0700 Subject: [PATCH] KVM: VMX: Drop pointless PI.NDST update when blocking Don't update Posted Interrupt's NDST, a.k.a. the target pCPU, in the pre-block path, as NDST is guaranteed to be up-to-date. The comment about the vCPU being preempted during the update is simply wrong, as the update path runs with IRQs disabled (from before snapshotting vcpu->cpu, until after the update completes). Since commit 8b306e2f3c41 ("KVM: VMX: avoid double list add with VT-d posted interrupts", 2017-09-27) The vCPU can get preempted _before_ the update starts, but not during. And if the vCPU is preempted before, vmx_vcpu_pi_load() is responsible for updating NDST when the vCPU is scheduled back in. In that case, the check against the wakeup vector in vmx_vcpu_pi_load() cannot be true as that would require the notification vector to have been set to the wakeup vector _before_ blocking. Opportunistically switch to using vcpu->cpu for the list/lock lookups, which do not need pre_pcpu since the same commit. Signed-off-by: Sean Christopherson Message-Id: <20211009021236.4122790-25-seanjc@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/vmx/posted_intr.c | 23 +++-------------------- 1 file changed, 3 insertions(+), 20 deletions(-) diff --git a/arch/x86/kvm/vmx/posted_intr.c b/arch/x86/kvm/vmx/posted_intr.c index 8abd5d891bde..bb93e9637494 100644 --- a/arch/x86/kvm/vmx/posted_intr.c +++ b/arch/x86/kvm/vmx/posted_intr.c @@ -135,7 +135,6 @@ static void __pi_post_block(struct kvm_vcpu *vcpu) * - Store the vCPU to the wakeup list, so when interrupts happen * we can find the right vCPU to wake up. * - Change the Posted-interrupt descriptor as below: - * 'NDST' <-- vcpu->pre_pcpu * 'NV' <-- POSTED_INTR_WAKEUP_VECTOR * - If 'ON' is set during this process, which means at least one * interrupt is posted for this vCPU, we cannot block it, in @@ -144,7 +143,6 @@ static void __pi_post_block(struct kvm_vcpu *vcpu) */ int pi_pre_block(struct kvm_vcpu *vcpu) { - unsigned int dest; struct pi_desc old, new; struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu); @@ -156,10 +154,10 @@ int pi_pre_block(struct kvm_vcpu *vcpu) local_irq_disable(); vcpu->pre_pcpu = vcpu->cpu; - spin_lock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu)); + spin_lock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->cpu)); list_add_tail(&vcpu->blocked_vcpu_list, - &per_cpu(blocked_vcpu_on_cpu, vcpu->pre_pcpu)); - spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu)); + &per_cpu(blocked_vcpu_on_cpu, vcpu->cpu)); + spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->cpu)); do { old.control = new.control = pi_desc->control; @@ -168,21 +166,6 @@ int pi_pre_block(struct kvm_vcpu *vcpu) "Warning: SN field of posted-interrupts " "is set before blocking\n"); - /* - * Since vCPU can be preempted during this process, - * vcpu->cpu could be different with pre_pcpu, we - * need to set pre_pcpu as the destination of wakeup - * notification event, then we can find the right vCPU - * to wakeup in wakeup handler if interrupts happen - * when the vCPU is in blocked state. - */ - dest = cpu_physical_id(vcpu->pre_pcpu); - - if (x2apic_mode) - new.ndst = dest; - else - new.ndst = (dest << 8) & 0xFF00; - /* set 'NV' to 'wakeup vector' */ new.nv = POSTED_INTR_WAKEUP_VECTOR; } while (cmpxchg64(&pi_desc->control, old.control, -- 2.11.0