From e295d2e7fbe69ddec772c951c466dfbfc1c96818 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 11 Jun 2025 14:35:40 -0700 Subject: 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 --- include/linux/kvm_host.h | 4 ---- 1 file changed, 4 deletions(-) (limited to 'include/linux') diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 3bde4fb5c6aa..9461517b4e62 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 -- cgit v1.2.3