KVM: x86: Split the APIC from the rest of IRQCHIP.

First patch in a series which enables the relocation of the
PIC/IOAPIC to userspace.

Adds capability KVM_CAP_SPLIT_IRQCHIP;

KVM_CAP_SPLIT_IRQCHIP enables the construction of LAPICs without the
rest of the irqchip.

Compile tested for x86.

Signed-off-by: Steve Rutherford <srutherford@google.com>
Suggested-by: Andrew Honig <ahonig@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

7 files changed, 56 insertions, 7 deletions

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index a0ef289d5a86..befcf555bddc 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -684,6 +684,8 @@ struct kvm_arch {
 	u32 bsp_vcpu_id;
 
 	u64 disabled_quirks;
+
+	bool irqchip_split;
 };
 
 struct kvm_vm_stat {
diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index f90952f64e79..08116ff227cc 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -35,6 +35,7 @@
 #include <linux/kvm_host.h>
 #include <linux/slab.h>
 
+#include "ioapic.h"
 #include "irq.h"
 #include "i8254.h"
 #include "x86.h"
@@ -333,7 +334,8 @@ static void create_pit_timer(struct kvm *kvm, u32 val, int is_period)
 	struct kvm_kpit_state *ps = &kvm->arch.vpit->pit_state;
 	s64 interval;
 
-	if (!irqchip_in_kernel(kvm) || ps->flags & KVM_PIT_FLAGS_HPET_LEGACY)
+	if (!ioapic_in_kernel(kvm) ||
+	    ps->flags & KVM_PIT_FLAGS_HPET_LEGACY)
 		return;
 
 	interval = muldiv64(val, NSEC_PER_SEC, KVM_PIT_FREQ);
diff --git a/arch/x86/kvm/ioapic.h b/arch/x86/kvm/ioapic.h
index bf36d66a1951..a8842c0dee73 100644
--- a/arch/x86/kvm/ioapic.h
+++ b/arch/x86/kvm/ioapic.h
@@ -97,6 +97,14 @@ static inline struct kvm_ioapic *ioapic_irqchip(struct kvm *kvm)
 	return kvm->arch.vioapic;
 }
 
+static inline int ioapic_in_kernel(struct kvm *kvm)
+{
+	int ret;
+
+	ret = (ioapic_irqchip(kvm) != NULL);
+	return ret;
+}
+
 void kvm_rtc_eoi_tracking_restore_one(struct kvm_vcpu *vcpu);
 bool kvm_apic_match_dest(struct kvm_vcpu *vcpu, struct kvm_lapic *source,
 		int short_hand, unsigned int dest, int dest_mode);
diff --git a/arch/x86/kvm/irq.h b/arch/x86/kvm/irq.h
index 9e6e7e04de98..2f9703dcd913 100644
--- a/arch/x86/kvm/irq.h
+++ b/arch/x86/kvm/irq.h
@@ -83,13 +83,22 @@ static inline struct kvm_pic *pic_irqchip(struct kvm *kvm)
 	return kvm->arch.vpic;
 }
 
+static inline int irqchip_split(struct kvm *kvm)
+{
+	return kvm->arch.irqchip_split;
+}
+
 static inline int irqchip_in_kernel(struct kvm *kvm)
 {
 	struct kvm_pic *vpic = pic_irqchip(kvm);
+	bool ret;
+
+	ret = (vpic != NULL);
+	ret |= irqchip_split(kvm);
 
 	/* Read vpic before kvm->irq_routing.  */
 	smp_rmb();
-	return vpic != NULL;
+	return ret;
 }
 
 static inline int lapic_in_kernel(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
index 9efff9e5b58c..67f6b62a6814 100644
--- a/arch/x86/kvm/irq_comm.c
+++ b/arch/x86/kvm/irq_comm.c
@@ -208,7 +208,7 @@ void kvm_free_irq_source_id(struct kvm *kvm, int irq_source_id)
 		goto unlock;
 	}
 	clear_bit(irq_source_id, &kvm->arch.irq_sources_bitmap);
-	if (!irqchip_in_kernel(kvm))
+	if (!ioapic_in_kernel(kvm))
 		goto unlock;
 
 	kvm_ioapic_clear_all(kvm->arch.vioapic, irq_source_id);
@@ -328,3 +328,10 @@ int kvm_setup_default_irq_routing(struct kvm *kvm)
 	return kvm_set_irq_routing(kvm, default_routing,
 				   ARRAY_SIZE(default_routing), 0);
 }
+
+static const struct kvm_irq_routing_entry empty_routing[] = {};
+
+int kvm_setup_empty_irq_routing(struct kvm *kvm)
+{
+	return kvm_set_irq_routing(kvm, empty_routing, 0, 0);
+}
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index c4bcc86d6dc4..e05946c36b87 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -209,7 +209,8 @@ out:
 	if (old)
 		kfree_rcu(old, rcu);
 
-	kvm_vcpu_request_scan_ioapic(kvm);
+	if (ioapic_in_kernel(kvm))
+		kvm_vcpu_request_scan_ioapic(kvm);
 }
 
 static inline void apic_set_spiv(struct kvm_lapic *apic, u32 val)
@@ -1845,7 +1846,8 @@ void kvm_apic_post_state_restore(struct kvm_vcpu *vcpu,
 		kvm_x86_ops->hwapic_isr_update(vcpu->kvm,
 				apic_find_highest_isr(apic));
 	kvm_make_request(KVM_REQ_EVENT, vcpu);
-	kvm_rtc_eoi_tracking_restore_one(vcpu);
+	if (ioapic_in_kernel(vcpu->kvm))
+		kvm_rtc_eoi_tracking_restore_one(vcpu);
 }
 
 void __kvm_migrate_apic_timer(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 28c98c8f9d1c..f720774a4797 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2448,6 +2448,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_ENABLE_CAP_VM:
 	case KVM_CAP_DISABLE_QUIRKS:
 	case KVM_CAP_SET_BOOT_CPU_ID:
+ 	case KVM_CAP_SPLIT_IRQCHIP:
 #ifdef CONFIG_KVM_DEVICE_ASSIGNMENT
 	case KVM_CAP_ASSIGN_DEV_IRQ:
 	case KVM_CAP_PCI_2_3:
@@ -3555,6 +3556,24 @@ static int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 		kvm->arch.disabled_quirks = cap->args[0];
 		r = 0;
 		break;
+	case KVM_CAP_SPLIT_IRQCHIP: {
+		mutex_lock(&kvm->lock);
+		r = -EEXIST;
+		if (irqchip_in_kernel(kvm))
+			goto split_irqchip_unlock;
+		if (atomic_read(&kvm->online_vcpus))
+			goto split_irqchip_unlock;
+		r = kvm_setup_empty_irq_routing(kvm);
+		if (r)
+			goto split_irqchip_unlock;
+		/* Pairs with irqchip_in_kernel. */
+		smp_wmb();
+		kvm->arch.irqchip_split = true;
+		r = 0;
+split_irqchip_unlock:
+		mutex_unlock(&kvm->lock);
+		break;
+	}
 	default:
 		r = -EINVAL;
 		break;
@@ -3668,7 +3687,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
 		}
 
 		r = -ENXIO;
-		if (!irqchip_in_kernel(kvm))
+		if (!irqchip_in_kernel(kvm) || irqchip_split(kvm))
 			goto get_irqchip_out;
 		r = kvm_vm_ioctl_get_irqchip(kvm, chip);
 		if (r)
@@ -3692,7 +3711,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
 		}
 
 		r = -ENXIO;
-		if (!irqchip_in_kernel(kvm))
+		if (!irqchip_in_kernel(kvm) || irqchip_split(kvm))
 			goto set_irqchip_out;
 		r = kvm_vm_ioctl_set_irqchip(kvm, chip);
 		if (r)