[PATCH v3 23/62] KVM: SVM: Stop walking list of routing table entries when updating IRTE

Sean Christopherson
2025-06-11T22:47:35Z

Now that KVM explicitly passes the new/current GSI routing to
pi_update_irte(), simply use the provided routing entry and 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. this is subtly a glorified nop, as KVM allows at most one MSI per
GSI, the for-loop can only ever process one entry, and that entry is the
new/current entry (see the WARN_ON_ONCE() added by "KVM: x86: Pass new
routing entries and irqfd when updating IRTEs" to ensure @new matches the
entry found in the routing table).

Tested-by: Sairaj Kodilkar <sarunkod@amd.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/svm/avic.c | 109 ++++++++++++++++------------------------
1 file changed, 44 insertions(+), 65 deletions(-)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 6260bf3697ba..a83769bb8123 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -843,11 +843,10 @@ int avic_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;
- bool set = !!new;
- int idx, ret = 0;
+ struct vcpu_data vcpu_info;
+ struct vcpu_svm *svm = NULL;
+ int ret = 0;

if (!kvm_arch_has_assigned_device(kvm) || !kvm_arch_has_irq_bypass())
return 0;
@@ -859,72 +858,53 @@ int avic_pi_update_irte(struct kvm_kernel_irqfd *irqfd, struct kvm *kvm,
svm_ir_list_del(irqfd);

pr_debug("SVM: %s: host_irq=%#x, guest_irq=%#x, set=%#x\n",
- __func__, host_irq, guest_irq, set);
+ __func__, host_irq, guest_irq, !!new);

- idx = srcu_read_lock(&kvm->irq_srcu);
- irq_rt = srcu_dereference(kvm->irq_routing, &kvm->irq_srcu);
+ /**
+ * Here, we setup with legacy mode in the following cases:
+ * 1. When cannot target interrupt to a specific vcpu.
+ * 2. Unsetting posted interrupt.
+ * 3. APIC virtualization is disabled for the vcpu.
+ * 4. IRQ has incompatible delivery mode (SMI, INIT, etc)
+ */
+ if (new && new->type == KVM_IRQ_ROUTING_MSI &&
+ !get_pi_vcpu_info(kvm, new, &vcpu_info, &svm) &&
+ kvm_vcpu_apicv_active(&svm->vcpu)) {
+ struct amd_iommu_pi_data pi;

- 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;
- }
+ enable_remapped_mode = false;

- hlist_for_each_entry(e, &irq_rt->map[guest_irq], link) {
- struct vcpu_data vcpu_info;
- struct vcpu_svm *svm = NULL;
-
- if (e->type != KVM_IRQ_ROUTING_MSI)
- continue;
-
- WARN_ON_ONCE(new && memcmp(e, new, sizeof(*new)));
+ /*
+ * Try to enable guest_mode in IRTE. Note, the address
+ * of the vCPU's AVIC backing page is passed to the
+ * IOMMU via vcpu_info->pi_desc_addr.
+ */
+ pi.ga_tag = AVIC_GATAG(to_kvm_svm(kvm)->avic_vm_id,
+ svm->vcpu.vcpu_id);
+ pi.is_guest_mode = true;
+ pi.vcpu_data = &vcpu_info;
+ ret = irq_set_vcpu_affinity(host_irq, &pi);

/**
- * Here, we setup with legacy mode in the following cases:
- * 1. When cannot target interrupt to a specific vcpu.
- * 2. Unsetting posted interrupt.
- * 3. APIC virtualization is disabled for the vcpu.
- * 4. IRQ has incompatible delivery mode (SMI, INIT, etc)
+ * Here, we successfully setting up vcpu affinity in
+ * IOMMU guest mode. Now, we need to store the posted
+ * interrupt information in a per-vcpu ir_list so that
+ * we can reference to them directly when we update vcpu
+ * scheduling information in IOMMU irte.
*/
- if (!get_pi_vcpu_info(kvm, e, &vcpu_info, &svm) && set &&
- kvm_vcpu_apicv_active(&svm->vcpu)) {
- struct amd_iommu_pi_data pi;
-
- enable_remapped_mode = false;
-
- /*
- * Try to enable guest_mode in IRTE. Note, the address
- * of the vCPU's AVIC backing page is passed to the
- * IOMMU via vcpu_info->pi_desc_addr.
- */
- pi.ga_tag = AVIC_GATAG(to_kvm_svm(kvm)->avic_vm_id,
- svm->vcpu.vcpu_id);
- pi.is_guest_mode = true;
- pi.vcpu_data = &vcpu_info;
- ret = irq_set_vcpu_affinity(host_irq, &pi);
-
- /**
- * Here, we successfully setting up vcpu affinity in
- * IOMMU guest mode. Now, we need to store the posted
- * interrupt information in a per-vcpu ir_list so that
- * we can reference to them directly when we update vcpu
- * scheduling information in IOMMU irte.
- */
- if (!ret && pi.is_guest_mode)
- svm_ir_list_add(svm, irqfd, &pi);
- }
-
- if (!ret && svm) {
- trace_kvm_pi_irte_update(host_irq, svm->vcpu.vcpu_id,
- e->gsi, vcpu_info.vector,
- vcpu_info.pi_desc_addr, set);
- }
-
- if (ret < 0) {
- pr_err("%s: failed to update PI IRTE\n", __func__);
- goto out;
- }
+ if (!ret)
+ ret = svm_ir_list_add(svm, irqfd, &pi);
+ }
+
+ if (!ret && svm) {
+ trace_kvm_pi_irte_update(host_irq, svm->vcpu.vcpu_id,
+ guest_irq, vcpu_info.vector,
+ vcpu_info.pi_desc_addr, !!new);
+ }
+
+ if (ret < 0) {
+ pr_err("%s: failed to update PI IRTE\n", __func__);
+ goto out;
}

if (enable_remapped_mode)
@@ -932,7 +912,6 @@ int avic_pi_update_irte(struct kvm_kernel_irqfd *irqfd, struct kvm *kvm,
else
ret = 0;
out:
- srcu_read_unlock(&kvm->irq_srcu, idx);
return ret;
}

--
2.50.0.rc1.591.g9c95f17f64-goog