From e295d2e7fbe69ddec772c951c466dfbfc1c96818 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 11 Jun 2025 14:35:40 -0700 Subject: [PATCH] KVM: x86: Trigger I/O APIC route rescan in kvm_arch_irq_routing_update() Trigger the I/O APIC route rescan that's performed for a split IRQ chip after userspace updates IRQ routes in kvm_arch_irq_routing_update(), i.e. before dropping kvm->irq_lock. Calling kvm_make_all_cpus_request() under a mutex is perfectly safe, and the smp_wmb()+smp_mb__after_atomic() pair in __kvm_make_request()+kvm_check_request() ensures the new routing is visible to vCPUs prior to the request being visible to vCPUs. In all likelihood, commit b053b2aef25d ("KVM: x86: Add EOI exit bitmap inference") somewhat arbitrarily made the request outside of irq_lock to avoid holding irq_lock any longer than is strictly necessary. And then commit abdb080f7ac8 ("kvm/irqchip: kvm_arch_irq_routing_update renaming split") took the easy route of adding another arch hook instead of risking a functional change. Note, the call to synchronize_srcu_expedited() does NOT provide ordering guarantees with respect to vCPUs scanning the new routing; as above, the request infrastructure provides the necessary ordering. I.e. there's no need to wait for kvm_scan_ioapic_routes() to complete if it's actively running, because regardless of whether it grabs the old or new table, the vCPU will have another KVM_REQ_SCAN_IOAPIC pending, i.e. will rescan again and see the new mappings. Acked-by: Kai Huang Link: https://lore.kernel.org/r/20250611213557.294358-2-seanjc@google.com Signed-off-by: Sean Christopherson --- arch/x86/kvm/irq_comm.c | 10 +++------- include/linux/kvm_host.h | 4 ---- virt/kvm/irqchip.c | 2 -- 3 files changed, 3 insertions(+), 13 deletions(-) diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c index d6d792b5d1bdb..e2ae62ff9cc2e 100644 --- a/arch/x86/kvm/irq_comm.c +++ b/arch/x86/kvm/irq_comm.c @@ -395,13 +395,6 @@ int kvm_setup_default_irq_routing(struct kvm *kvm) ARRAY_SIZE(default_routing), 0); } -void kvm_arch_post_irq_routing_update(struct kvm *kvm) -{ - if (!irqchip_split(kvm)) - return; - kvm_make_scan_ioapic_request(kvm); -} - void kvm_scan_ioapic_irq(struct kvm_vcpu *vcpu, u32 dest_id, u16 dest_mode, u8 vector, unsigned long *ioapic_handled_vectors) { @@ -466,4 +459,7 @@ void kvm_arch_irq_routing_update(struct kvm *kvm) #ifdef CONFIG_KVM_HYPERV kvm_hv_irq_routing_update(kvm); #endif + + if (irqchip_split(kvm)) + kvm_make_scan_ioapic_request(kvm); } diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 3bde4fb5c6aa4..9461517b4e625 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -1024,14 +1024,10 @@ void vcpu_put(struct kvm_vcpu *vcpu); #ifdef __KVM_HAVE_IOAPIC void kvm_arch_post_irq_ack_notifier_list_update(struct kvm *kvm); -void kvm_arch_post_irq_routing_update(struct kvm *kvm); #else static inline void kvm_arch_post_irq_ack_notifier_list_update(struct kvm *kvm) { } -static inline void kvm_arch_post_irq_routing_update(struct kvm *kvm) -{ -} #endif #ifdef CONFIG_HAVE_KVM_IRQCHIP diff --git a/virt/kvm/irqchip.c b/virt/kvm/irqchip.c index 162d8ed889f21..6ccabfd32287e 100644 --- a/virt/kvm/irqchip.c +++ b/virt/kvm/irqchip.c @@ -222,8 +222,6 @@ int kvm_set_irq_routing(struct kvm *kvm, kvm_arch_irq_routing_update(kvm); mutex_unlock(&kvm->irq_lock); - kvm_arch_post_irq_routing_update(kvm); - synchronize_srcu_expedited(&kvm->irq_srcu); new = old; -- 2.47.2