KVM: x86: Use vector-hashing to deliver lowest-priority interrupts

Use vector-hashing to deliver lowest-priority interrupts, As an
example, modern Intel CPUs in server platform use this method to
handle lowest-priority interrupts.
Signed-off-by: Feng Wu <feng.wu@intel.com>
Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -754,6 +754,8 @@ struct kvm_arch {
 
 	bool irqchip_split;
 	u8 nr_reserved_ioapic_pins;
+
+	bool disabled_lapic_found;
 };
 
 struct kvm_vm_stat {

arch/x86/kvm/irq_comm.c

@@ -34,6 +34,7 @@
 #include "lapic.h"
 
 #include "hyperv.h"
+#include "x86.h"
 
 static int kvm_set_pic_irq(struct kvm_kernel_irq_routing_entry *e,
 			   struct kvm *kvm, int irq_source_id, int level,
@@ -57,6 +58,8 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
 {
 	int i, r = -1;
 	struct kvm_vcpu *vcpu, *lowest = NULL;
+	unsigned long dest_vcpu_bitmap[BITS_TO_LONGS(KVM_MAX_VCPUS)];
+	unsigned int dest_vcpus = 0;
 
 	if (irq->dest_mode == 0 && irq->dest_id == 0xff &&
 			kvm_lowest_prio_delivery(irq)) {
@@ -67,6 +70,8 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
 	if (kvm_irq_delivery_to_apic_fast(kvm, src, irq, &r, dest_map))
 		return r;
 
+	memset(dest_vcpu_bitmap, 0, sizeof(dest_vcpu_bitmap));
+
 	kvm_for_each_vcpu(i, vcpu, kvm) {
 		if (!kvm_apic_present(vcpu))
 			continue;
@@ -80,11 +85,23 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
 				r = 0;
 			r += kvm_apic_set_irq(vcpu, irq, dest_map);
 		} else if (kvm_lapic_enabled(vcpu)) {
+			if (!kvm_vector_hashing_enabled()) {
 				if (!lowest)
 					lowest = vcpu;
 				else if (kvm_apic_compare_prio(vcpu, lowest) < 0)
 					lowest = vcpu;
+			} else {
+				__set_bit(i, dest_vcpu_bitmap);
+				dest_vcpus++;
+			}
+		}
 	}
+
+	if (dest_vcpus != 0) {
+		int idx = kvm_vector_to_index(irq->vector, dest_vcpus,
+					dest_vcpu_bitmap, KVM_MAX_VCPUS);
+
+		lowest = kvm_get_vcpu(kvm, idx);
 	}
 
 	if (lowest)

arch/x86/kvm/lapic.c

@@ -675,6 +675,22 @@ bool kvm_apic_match_dest(struct kvm_vcpu *vcpu, struct kvm_lapic *source,
 	}
 }
 
+int kvm_vector_to_index(u32 vector, u32 dest_vcpus,
+		       const unsigned long *bitmap, u32 bitmap_size)
+{
+	u32 mod;
+	int i, idx = -1;
+
+	mod = vector % dest_vcpus;
+
+	for (i = 0; i <= mod; i++) {
+		idx = find_next_bit(bitmap, bitmap_size, idx + 1);
+		BUG_ON(idx == bitmap_size);
+	}
+
+	return idx;
+}
+
 bool kvm_irq_delivery_to_apic_fast(struct kvm *kvm, struct kvm_lapic *src,
 		struct kvm_lapic_irq *irq, int *r, unsigned long *dest_map)
 {
@@ -727,21 +743,49 @@ bool kvm_irq_delivery_to_apic_fast(struct kvm *kvm, struct kvm_lapic *src,
 
 		dst = map->logical_map[cid];
 
-		if (kvm_lowest_prio_delivery(irq)) {
+		if (!kvm_lowest_prio_delivery(irq))
+			goto set_irq;
+
+		if (!kvm_vector_hashing_enabled()) {
 			int l = -1;
 			for_each_set_bit(i, &bitmap, 16) {
 				if (!dst[i])
 					continue;
 				if (l < 0)
 					l = i;
-				else if (kvm_apic_compare_prio(dst[i]->vcpu, dst[l]->vcpu) < 0)
+				else if (kvm_apic_compare_prio(dst[i]->vcpu,
+							dst[l]->vcpu) < 0)
 					l = i;
 			}
-
 			bitmap = (l >= 0) ? 1 << l : 0;
+		} else {
+			int idx;
+			unsigned int dest_vcpus;
+
+			dest_vcpus = hweight16(bitmap);
+			if (dest_vcpus == 0)
+				goto out;
+
+			idx = kvm_vector_to_index(irq->vector,
+				dest_vcpus, &bitmap, 16);
+
+			/*
+			 * We may find a hardware disabled LAPIC here, if that
+			 * is the case, print out a error message once for each
+			 * guest and return.
+			 */
+			if (!dst[idx] && !kvm->arch.disabled_lapic_found) {
+				kvm->arch.disabled_lapic_found = true;
+				printk(KERN_INFO
+					"Disabled LAPIC found during irq injection\n");
+				goto out;
+			}
+
+			bitmap = (idx >= 0) ? 1 << idx : 0;
 		}
 	}
 
+set_irq:
 	for_each_set_bit(i, &bitmap, 16) {
 		if (!dst[i])
 			continue;

arch/x86/kvm/lapic.h

@@ -175,4 +175,6 @@ void wait_lapic_expire(struct kvm_vcpu *vcpu);
 
 bool kvm_intr_is_single_vcpu_fast(struct kvm *kvm, struct kvm_lapic_irq *irq,
 			struct kvm_vcpu **dest_vcpu);
+int kvm_vector_to_index(u32 vector, u32 dest_vcpus,
+			const unsigned long *bitmap, u32 bitmap_size);
 #endif

arch/x86/kvm/x86.c

@@ -123,6 +123,9 @@ module_param(tsc_tolerance_ppm, uint, S_IRUGO | S_IWUSR);
 unsigned int __read_mostly lapic_timer_advance_ns = 0;
 module_param(lapic_timer_advance_ns, uint, S_IRUGO | S_IWUSR);
 
+static bool __read_mostly vector_hashing = true;
+module_param(vector_hashing, bool, S_IRUGO);
+
 static bool __read_mostly backwards_tsc_observed = false;
 
 #define KVM_NR_SHARED_MSRS 16
@@ -8364,6 +8367,12 @@ int kvm_arch_update_irqfd_routing(struct kvm *kvm, unsigned int host_irq,
 	return kvm_x86_ops->update_pi_irte(kvm, host_irq, guest_irq, set);
 }
 
+bool kvm_vector_hashing_enabled(void)
+{
+	return vector_hashing;
+}
+EXPORT_SYMBOL_GPL(kvm_vector_hashing_enabled);
+
 EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_exit);
 EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_fast_mmio);
 EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_inj_virq);

arch/x86/kvm/x86.h

@@ -179,6 +179,7 @@ int kvm_mtrr_set_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data);
 int kvm_mtrr_get_msr(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata);
 bool kvm_mtrr_check_gfn_range_consistency(struct kvm_vcpu *vcpu, gfn_t gfn,
 					  int page_num);
+bool kvm_vector_hashing_enabled(void);
 
 #define KVM_SUPPORTED_XCR0     (XFEATURE_MASK_FP | XFEATURE_MASK_SSE \
 				| XFEATURE_MASK_YMM | XFEATURE_MASK_BNDREGS \