[PATCH v2 2/2] KVM: x86: Add lowest-priority support for vt-d posted-interrupts

[Feng Wu]

Use vector-hashing to deliver lowest-priority interrupts for
VT-d posted-interrupts.

Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
---
 arch/x86/kvm/lapic.c | 67 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 arch/x86/kvm/lapic.h |  2 ++
 arch/x86/kvm/vmx.c   | 12 ++++++++--
 3 files changed, 79 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index e29001f..d4f2c8f 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -854,6 +854,73 @@ out:
 }
 
 /*
+ * This routine handles lowest-priority interrupts using vector-hashing
+ * mechanism. As an example, modern Intel CPUs use this method to handle
+ * lowest-priority interrupts.
+ *
+ * Here is the details about the vector-hashing mechanism:
+ * 1. For lowest-priority interrupts, store all the possible destination
+ *    vCPUs in an array.
+ * 2. Use "guest vector % max number of destination vCPUs" to find the right
+ *    destination vCPU in the array for the lowest-priority interrupt.
+ */
+struct kvm_vcpu *kvm_intr_vector_hashing_dest(struct kvm *kvm,
+					      struct kvm_lapic_irq *irq)
+{
+	struct kvm_apic_map *map;
+	struct kvm_vcpu *vcpu = NULL;
+
+	if (irq->shorthand)
+		return NULL;
+
+	rcu_read_lock();
+	map = rcu_dereference(kvm->arch.apic_map);
+
+	if (!map)
+		goto out;
+
+	if ((irq->dest_mode != APIC_DEST_PHYSICAL) &&
+			kvm_lowest_prio_delivery(irq)) {
+		u16 cid;
+		int i, idx = 0;
+		unsigned long bitmap = 1;
+		unsigned int dest_vcpus = 0;
+		struct kvm_lapic **dst = NULL;
+
+
+		if (!kvm_apic_logical_map_valid(map))
+			goto out;
+
+		apic_logical_id(map, irq->dest_id, &cid, (u16 *)&bitmap);
+
+		if (cid >= ARRAY_SIZE(map->logical_map))
+			goto out;
+
+		dst = map->logical_map[cid];
+
+		for_each_set_bit(i, &bitmap, 16) {
+			if (!dst[i] && !kvm_lapic_enabled(dst[i]->vcpu)) {
+				clear_bit(i, &bitmap);
+				continue;
+			}
+		}
+
+		dest_vcpus = hweight16(bitmap);
+
+		if (dest_vcpus != 0) {
+			idx = kvm_vector_2_index(irq->vector, dest_vcpus,
+						 &bitmap, 16);
+			vcpu = dst[idx-1]->vcpu;
+		}
+	}
+
+out:
+	rcu_read_unlock();
+	return vcpu;
+}
+EXPORT_SYMBOL_GPL(kvm_intr_vector_hashing_dest);
+
+/*
  * Add a pending IRQ into lapic.
  * Return 1 if successfully added and 0 if discarded.
  */
diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
index 6890ef0..52bffce 100644
--- a/arch/x86/kvm/lapic.h
+++ b/arch/x86/kvm/lapic.h
@@ -172,4 +172,6 @@ bool kvm_intr_is_single_vcpu_fast(struct kvm *kvm, struct kvm_lapic_irq *irq,
 			struct kvm_vcpu **dest_vcpu);
 int kvm_vector_2_index(u32 vector, u32 dest_vcpus,
 		       const unsigned long *bitmap, u32 bitmap_size);
+struct kvm_vcpu *kvm_intr_vector_hashing_dest(struct kvm *kvm,
+					      struct kvm_lapic_irq *irq);
 #endif
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 5eb56ed..3f89189 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -10702,8 +10702,16 @@ static int vmx_update_pi_irte(struct kvm *kvm, unsigned int host_irq,
 		 */
 
 		kvm_set_msi_irq(e, &irq);
-		if (!kvm_intr_is_single_vcpu(kvm, &irq, &vcpu))
-			continue;
+
+		if (!kvm_intr_is_single_vcpu(kvm, &irq, &vcpu)) {
+			if (!kvm_vector_hashing_enabled() ||
+					irq.delivery_mode != APIC_DM_LOWEST)
+				continue;
+
+			vcpu = kvm_intr_vector_hashing_dest(kvm, &irq);
+			if (!vcpu)
+				continue;
+		}
 
 		vcpu_info.pi_desc_addr = __pa(vcpu_to_pi_desc(vcpu));
 		vcpu_info.vector = irq.vector;
-- 
2.1.0

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