From: Sean Christopherson Date: Tue, 28 Apr 2026 15:50:43 +0000 (-0700) Subject: KVM: x86: Fix misleading variable names and add more comments for PIR=>IRR flow X-Git-Tag: v7.1-rc3~44^2~1 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=0aec99f9bf0213f7910688472e1ccf517c0e8b5a;p=thirdparty%2Flinux.git KVM: x86: Fix misleading variable names and add more comments for PIR=>IRR flow Rename kvm_apic_update_irr()'s "irr_updated" and vmx_sync_pir_to_irr()'s "got_posted_interrupt" to a more accurate "max_irr_is_from_pir", as neither "irr_updated" nor "got_posted_interrupt" is accurate. __kvm_apic_update_irr() and thus kvm_apic_update_irr() specifically return true if and only if the highest priority IRQ, i.e. max_irr, is a "new" pending IRQ from the PIR. I.e. it's possible for the IRR to be updated, i.e. for a posted IRQ to be "got", *without* the APIs returning true. Expand vmx_sync_pir_to_irr()'s comment to explain why it's necessary to set KVM_REQ_EVENT only if a "new" IRQ was found, and to explain why it's safe to do so only if a new IRQ is also the highest priority pending IRQ. No functional change intended. Signed-off-by: Sean Christopherson Link: https://patch.msgid.link/20260503201703.108231-3-pbonzini@redhat.com/ Signed-off-by: Paolo Bonzini --- diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 5ee14d6bc2883..4078e624ca667 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -667,14 +667,14 @@ bool __kvm_apic_update_irr(unsigned long *pir, void *regs, int *max_irr) u32 *__pir = (void *)pir_vals; u32 i, vec; u32 irr_val, prev_irr_val; - int max_updated_irr; + int max_new_irr; if (!pi_harvest_pir(pir, pir_vals)) { *max_irr = apic_find_highest_vector(regs + APIC_IRR); return false; } - max_updated_irr = -1; + max_new_irr = -1; *max_irr = -1; for (i = vec = 0; i <= 7; i++, vec += 32) { @@ -690,25 +690,25 @@ bool __kvm_apic_update_irr(unsigned long *pir, void *regs, int *max_irr) !try_cmpxchg(p_irr, &prev_irr_val, irr_val)); if (prev_irr_val != irr_val) - max_updated_irr = __fls(irr_val ^ prev_irr_val) + vec; + max_new_irr = __fls(irr_val ^ prev_irr_val) + vec; } if (irr_val) *max_irr = __fls(irr_val) + vec; } - return ((max_updated_irr != -1) && - (max_updated_irr == *max_irr)); + return max_new_irr != -1 && max_new_irr == *max_irr; } EXPORT_SYMBOL_FOR_KVM_INTERNAL(__kvm_apic_update_irr); bool kvm_apic_update_irr(struct kvm_vcpu *vcpu, unsigned long *pir, int *max_irr) { struct kvm_lapic *apic = vcpu->arch.apic; - bool irr_updated = __kvm_apic_update_irr(pir, apic->regs, max_irr); + bool max_irr_is_from_pir; - if (unlikely(!apic->apicv_active && irr_updated)) + max_irr_is_from_pir = __kvm_apic_update_irr(pir, apic->regs, max_irr); + if (unlikely(!apic->apicv_active && max_irr_is_from_pir)) apic->irr_pending = true; - return irr_updated; + return max_irr_is_from_pir; } EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_apic_update_irr); diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index a29896a9ef145..5c2c33a5f7dc9 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -7029,8 +7029,8 @@ static void vmx_set_rvi(int vector) int vmx_sync_pir_to_irr(struct kvm_vcpu *vcpu) { struct vcpu_vt *vt = to_vt(vcpu); + bool max_irr_is_from_pir; int max_irr; - bool got_posted_interrupt; if (KVM_BUG_ON(!enable_apicv, vcpu->kvm)) return -EIO; @@ -7042,17 +7042,22 @@ int vmx_sync_pir_to_irr(struct kvm_vcpu *vcpu) * But on x86 this is just a compiler barrier anyway. */ smp_mb__after_atomic(); - got_posted_interrupt = - kvm_apic_update_irr(vcpu, vt->pi_desc.pir, &max_irr); + max_irr_is_from_pir = kvm_apic_update_irr(vcpu, vt->pi_desc.pir, + &max_irr); } else { max_irr = kvm_lapic_find_highest_irr(vcpu); - got_posted_interrupt = false; + max_irr_is_from_pir = false; } /* - * Newly recognized interrupts are injected via either virtual interrupt - * delivery (RVI) or KVM_REQ_EVENT. Virtual interrupt delivery is - * disabled in two cases: + * If APICv is enabled and L2 is not active, then update the Requesting + * Virtual Interrupt (RVI) portion of vmcs01.GUEST_INTR_STATUS with the + * highest priority IRR to deliver the IRQ via Virtual Interrupt + * Delivery. Note, this is required even if the highest priority IRQ + * was already pending in the IRR, as RVI isn't updated in lockstep with + * the IRR (unlike apic->irr_pending). + * + * For the cases where Virtual Interrupt Delivery can't be used: * * 1) If L2 is running and the vCPU has a new pending interrupt. If L1 * wants to exit on interrupts, KVM_REQ_EVENT is needed to synthesize a @@ -7063,10 +7068,29 @@ int vmx_sync_pir_to_irr(struct kvm_vcpu *vcpu) * 2) If APICv is disabled for this vCPU, assigned devices may still * attempt to post interrupts. The posted interrupt vector will cause * a VM-Exit and the subsequent entry will call sync_pir_to_irr. + * + * In both cases, set KVM_REQ_EVENT if and only if the highest priority + * pending IRQ came from the PIR, as setting KVM_REQ_EVENT if any IRQ + * is pending may put the vCPU into an infinite loop, e.g. if the IRQ + * is blocked, then it will stay pending until an IRQ window is opened. + * + * Note! It's possible that one or more IRQs were moved from the PIR + * to the IRR _without_ max_irr_is_from_pir being true! I.e. if there + * was a higher priority IRQ already pending in the IRR. Not setting + * KVM_REQ_EVENT in this case is intentional and safe. If APICv is + * inactive, or L2 is running with exit-on-interrupt off (in vmcs12), + * i.e. without nested virtual interrupt delivery, then there's no need + * to request an IRQ window as the lower priority IRQ only needs to be + * delivered when the higher priority IRQ is dismissed from the ISR, + * i.e. on the next EOI, and EOIs are always intercepted if APICv is + * disabled or if L2 is running without nested VID. If L2 is running + * exit-on-interrupt on (in vmcs12), then the higher priority IRQ will + * trigger a nested VM-Exit, at which point KVM will re-evaluate L1's + * pending IRQs. */ if (!is_guest_mode(vcpu) && kvm_vcpu_apicv_active(vcpu)) vmx_set_rvi(max_irr); - else if (got_posted_interrupt) + else if (max_irr_is_from_pir) kvm_make_request(KVM_REQ_EVENT, vcpu); return max_irr;