[PATCH v3 24/62] KVM: VMX: Stop walking list of routing table entries when updating IRTE

Sean Christopherson
2025-06-11T22:47:37Z

Now that KVM provides the to-be-updated routing entry, stop walking the
routing table to find that entry. KVM, via setup_routing_entry() and
sanity checked by kvm_get_msi_route(), disallows having a GSI configured
to trigger multiple MSIs, i.e. the for-loop can only process one entry.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/vmx/posted_intr.c | 100 +++++++++++----------------------
1 file changed, 33 insertions(+), 67 deletions(-)

diff --git a/arch/x86/kvm/vmx/posted_intr.c b/arch/x86/kvm/vmx/posted_intr.c
index d4826a6b674f..e59eae11f476 100644
--- a/arch/x86/kvm/vmx/posted_intr.c
+++ b/arch/x86/kvm/vmx/posted_intr.c
@@ -302,78 +302,44 @@ int vmx_pi_update_irte(struct kvm_kernel_irqfd *irqfd, struct kvm *kvm,
unsigned int host_irq, uint32_t guest_irq,
struct kvm_kernel_irq_routing_entry *new)
{
- struct kvm_kernel_irq_routing_entry *e;
- struct kvm_irq_routing_table *irq_rt;
- bool enable_remapped_mode = true;
struct kvm_lapic_irq irq;
struct kvm_vcpu *vcpu;
struct vcpu_data vcpu_info;
- bool set = !!new;
- int idx, ret = 0;

if (!vmx_can_use_vtd_pi(kvm))
return 0;

- idx = srcu_read_lock(&kvm->irq_srcu);
- irq_rt = srcu_dereference(kvm->irq_routing, &kvm->irq_srcu);
- if (guest_irq >= irq_rt->nr_rt_entries ||
- hlist_empty(&irq_rt->map[guest_irq])) {
- pr_warn_once("no route for guest_irq %u/%u (broken user space?)\n",
- guest_irq, irq_rt->nr_rt_entries);
- goto out;
- }
-
- hlist_for_each_entry(e, &irq_rt->map[guest_irq], link) {
- if (e->type != KVM_IRQ_ROUTING_MSI)
- continue;
-
- WARN_ON_ONCE(new && memcmp(e, new, sizeof(*new)));
-
- /*
- * VT-d PI cannot support posting multicast/broadcast
- * interrupts to a vCPU, we still use interrupt remapping
- * for these kind of interrupts.
- *
- * For lowest-priority interrupts, we only support
- * those with single CPU as the destination, e.g. user
- * configures the interrupts via /proc/irq or uses
- * irqbalance to make the interrupts single-CPU.
- *
- * We will support full lowest-priority interrupt later.
- *
- * In addition, we can only inject generic interrupts using
- * the PI mechanism, refuse to route others through it.
- */
-
- kvm_set_msi_irq(kvm, e, &irq);
- if (!kvm_intr_is_single_vcpu(kvm, &irq, &vcpu) ||
- !kvm_irq_is_postable(&irq))
- continue;
-
- vcpu_info.pi_desc_addr = __pa(vcpu_to_pi_desc(vcpu));
- vcpu_info.vector = irq.vector;
-
- trace_kvm_pi_irte_update(host_irq, vcpu->vcpu_id, e->gsi,
- vcpu_info.vector, vcpu_info.pi_desc_addr, set);
-
- if (!set)
- continue;
-
- enable_remapped_mode = false;
-
- ret = irq_set_vcpu_affinity(host_irq, &vcpu_info);
- if (ret < 0) {
- printk(KERN_INFO "%s: failed to update PI IRTE\n",
- __func__);
- goto out;
- }
- }
-
- if (enable_remapped_mode)
- ret = irq_set_vcpu_affinity(host_irq, NULL);
-
- ret = 0;
-out:
- srcu_read_unlock(&kvm->irq_srcu, idx);
- return ret;
+ /*
+ * VT-d PI cannot support posting multicast/broadcast
+ * interrupts to a vCPU, we still use interrupt remapping
+ * for these kind of interrupts.
+ *
+ * For lowest-priority interrupts, we only support
+ * those with single CPU as the destination, e.g. user
+ * configures the interrupts via /proc/irq or uses
+ * irqbalance to make the interrupts single-CPU.
+ *
+ * We will support full lowest-priority interrupt later.
+ *
+ * In addition, we can only inject generic interrupts using
+ * the PI mechanism, refuse to route others through it.
+ */
+ if (!new || new->type != KVM_IRQ_ROUTING_MSI)
+ goto do_remapping;
+
+ kvm_set_msi_irq(kvm, new, &irq);
+
+ if (!kvm_intr_is_single_vcpu(kvm, &irq, &vcpu) ||
+ !kvm_irq_is_postable(&irq))
+ goto do_remapping;
+
+ vcpu_info.pi_desc_addr = __pa(vcpu_to_pi_desc(vcpu));
+ vcpu_info.vector = irq.vector;
+
+ trace_kvm_pi_irte_update(host_irq, vcpu->vcpu_id, guest_irq,
+ vcpu_info.vector, vcpu_info.pi_desc_addr, true);
+
+ return irq_set_vcpu_affinity(host_irq, &vcpu_info);
+do_remapping:
+ return irq_set_vcpu_affinity(host_irq, NULL);
}
--
2.50.0.rc1.591.g9c95f17f64-goog