KVM: X86: Implement PV IPIs in linux guest

Implement paravirtual apic hooks to enable PV IPIs for KVM if the "send IPI"
hypercall is available.  The hypercall lets a guest send IPIs, with
at most 128 destinations per hypercall in 64-bit mode and 64 vCPUs per
hypercall in 32-bit mode.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/uapi/asm/kvm_para.h

@@ -28,6 +28,7 @@
 #define KVM_FEATURE_PV_UNHALT		7
 #define KVM_FEATURE_PV_TLB_FLUSH	9
 #define KVM_FEATURE_ASYNC_PF_VMEXIT	10
+#define KVM_FEATURE_PV_SEND_IPI	11
 
 #define KVM_HINTS_REALTIME      0
 

arch/x86/kernel/kvm.c

@@ -454,6 +454,98 @@ static void __init sev_map_percpu_data(void)
 }
 
 #ifdef CONFIG_SMP
+#define KVM_IPI_CLUSTER_SIZE	(2 * BITS_PER_LONG)
+
+static void __send_ipi_mask(const struct cpumask *mask, int vector)
+{
+	unsigned long flags;
+	int cpu, apic_id, icr;
+	int min = 0, max = 0;
+#ifdef CONFIG_X86_64
+	__uint128_t ipi_bitmap = 0;
+#else
+	u64 ipi_bitmap = 0;
+#endif
+
+	if (cpumask_empty(mask))
+		return;
+
+	local_irq_save(flags);
+
+	switch (vector) {
+	default:
+		icr = APIC_DM_FIXED | vector;
+		break;
+	case NMI_VECTOR:
+		icr = APIC_DM_NMI;
+		break;
+	}
+
+	for_each_cpu(cpu, mask) {
+		apic_id = per_cpu(x86_cpu_to_apicid, cpu);
+		if (!ipi_bitmap) {
+			min = max = apic_id;
+		} else if (apic_id < min && max - apic_id < KVM_IPI_CLUSTER_SIZE) {
+			ipi_bitmap <<= min - apic_id;
+			min = apic_id;
+		} else if (apic_id < min + KVM_IPI_CLUSTER_SIZE) {
+			max = apic_id < max ? max : apic_id;
+		} else {
+			kvm_hypercall4(KVM_HC_SEND_IPI, (unsigned long)ipi_bitmap,
+				(unsigned long)(ipi_bitmap >> BITS_PER_LONG), min, icr);
+			min = max = apic_id;
+			ipi_bitmap = 0;
+		}
+		__set_bit(apic_id - min, (unsigned long *)&ipi_bitmap);
+	}
+
+	if (ipi_bitmap) {
+		kvm_hypercall4(KVM_HC_SEND_IPI, (unsigned long)ipi_bitmap,
+			(unsigned long)(ipi_bitmap >> BITS_PER_LONG), min, icr);
+	}
+
+	local_irq_restore(flags);
+}
+
+static void kvm_send_ipi_mask(const struct cpumask *mask, int vector)
+{
+	__send_ipi_mask(mask, vector);
+}
+
+static void kvm_send_ipi_mask_allbutself(const struct cpumask *mask, int vector)
+{
+	unsigned int this_cpu = smp_processor_id();
+	struct cpumask new_mask;
+	const struct cpumask *local_mask;
+
+	cpumask_copy(&new_mask, mask);
+	cpumask_clear_cpu(this_cpu, &new_mask);
+	local_mask = &new_mask;
+	__send_ipi_mask(local_mask, vector);
+}
+
+static void kvm_send_ipi_allbutself(int vector)
+{
+	kvm_send_ipi_mask_allbutself(cpu_online_mask, vector);
+}
+
+static void kvm_send_ipi_all(int vector)
+{
+	__send_ipi_mask(cpu_online_mask, vector);
+}
+
+/*
+ * Set the IPI entry points
+ */
+static void kvm_setup_pv_ipi(void)
+{
+	apic->send_IPI_mask = kvm_send_ipi_mask;
+	apic->send_IPI_mask_allbutself = kvm_send_ipi_mask_allbutself;
+	apic->send_IPI_allbutself = kvm_send_ipi_allbutself;
+	apic->send_IPI_all = kvm_send_ipi_all;
+	pr_info("KVM setup pv IPIs\n");
+}
+
 static void __init kvm_smp_prepare_cpus(unsigned int max_cpus)
 {
 	native_smp_prepare_cpus(max_cpus);
@@ -626,6 +718,10 @@ static uint32_t __init kvm_detect(void)
 
 static void __init kvm_apic_init(void)
 {
+#if defined(CONFIG_SMP)
+	if (kvm_para_has_feature(KVM_FEATURE_PV_SEND_IPI))
+		kvm_setup_pv_ipi();
+#endif
 }
 
 static void __init kvm_init_platform(void)

include/uapi/linux/kvm_para.h

@@ -27,6 +27,7 @@
 #define KVM_HC_MIPS_EXIT_VM		7
 #define KVM_HC_MIPS_CONSOLE_OUTPUT	8
 #define KVM_HC_CLOCK_PAIRING		9
+#define KVM_HC_SEND_IPI		10
 
 /*
  * hypercalls use architecture specific