KVM: x86: Add support for saving&restoring debug registers

So far user space was not able to save and restore debug registers for
migration or after reset. Plug this hole.
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

Documentation/kvm/api.txt

@@ -718,6 +718,37 @@ If KVM_CAP_INTR_SHADOW is available, KVM_VCPUEVENT_VALID_SHADOW can be set in
 the flags field to signal that interrupt.shadow contains a valid state and
 shall be written into the VCPU.
 
+4.32 KVM_GET_DEBUGREGS
+
+Capability: KVM_CAP_DEBUGREGS
+Architectures: x86
+Type: vm ioctl
+Parameters: struct kvm_debugregs (out)
+Returns: 0 on success, -1 on error
+
+Reads debug registers from the vcpu.
+
+struct kvm_debugregs {
+	__u64 db[4];
+	__u64 dr6;
+	__u64 dr7;
+	__u64 flags;
+	__u64 reserved[9];
+};
+
+4.33 KVM_SET_DEBUGREGS
+
+Capability: KVM_CAP_DEBUGREGS
+Architectures: x86
+Type: vm ioctl
+Parameters: struct kvm_debugregs (in)
+Returns: 0 on success, -1 on error
+
+Writes debug registers into the vcpu.
+
+See KVM_GET_DEBUGREGS for the data structure. The flags field is unused
+yet and must be cleared on entry.
+
 
 5. The kvm_run structure
 

arch/x86/include/asm/kvm.h

@@ -21,6 +21,7 @@
 #define __KVM_HAVE_PIT_STATE2
 #define __KVM_HAVE_XEN_HVM
 #define __KVM_HAVE_VCPU_EVENTS
+#define __KVM_HAVE_DEBUGREGS
 
 /* Architectural interrupt line count. */
 #define KVM_NR_INTERRUPTS 256
@@ -289,4 +290,13 @@ struct kvm_vcpu_events {
 	__u32 reserved[10];
 };
 
+/* for KVM_GET/SET_DEBUGREGS */
+struct kvm_debugregs {
+	__u64 db[4];
+	__u64 dr6;
+	__u64 dr7;
+	__u64 flags;
+	__u64 reserved[9];
+};
+
 #endif /* _ASM_X86_KVM_H */

arch/x86/kvm/x86.c

@@ -1548,6 +1548,7 @@ int kvm_dev_ioctl_check_extension(long ext)
 	case KVM_CAP_HYPERV_VAPIC:
 	case KVM_CAP_HYPERV_SPIN:
 	case KVM_CAP_PCI_SEGMENT:
+	case KVM_CAP_DEBUGREGS:
 	case KVM_CAP_X86_ROBUST_SINGLESTEP:
 		r = 1;
 		break;
@@ -2165,6 +2166,36 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
 	return 0;
 }
 
+static void kvm_vcpu_ioctl_x86_get_debugregs(struct kvm_vcpu *vcpu,
+					     struct kvm_debugregs *dbgregs)
+{
+	vcpu_load(vcpu);
+
+	memcpy(dbgregs->db, vcpu->arch.db, sizeof(vcpu->arch.db));
+	dbgregs->dr6 = vcpu->arch.dr6;
+	dbgregs->dr7 = vcpu->arch.dr7;
+	dbgregs->flags = 0;
+
+	vcpu_put(vcpu);
+}
+
+static int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu,
+					    struct kvm_debugregs *dbgregs)
+{
+	if (dbgregs->flags)
+		return -EINVAL;
+
+	vcpu_load(vcpu);
+
+	memcpy(vcpu->arch.db, dbgregs->db, sizeof(vcpu->arch.db));
+	vcpu->arch.dr6 = dbgregs->dr6;
+	vcpu->arch.dr7 = dbgregs->dr7;
+
+	vcpu_put(vcpu);
+
+	return 0;
+}
+
 long kvm_arch_vcpu_ioctl(struct file *filp,
 			 unsigned int ioctl, unsigned long arg)
 {
@@ -2343,6 +2374,29 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 		r = kvm_vcpu_ioctl_x86_set_vcpu_events(vcpu, &events);
 		break;
 	}
+	case KVM_GET_DEBUGREGS: {
+		struct kvm_debugregs dbgregs;
+
+		kvm_vcpu_ioctl_x86_get_debugregs(vcpu, &dbgregs);
+
+		r = -EFAULT;
+		if (copy_to_user(argp, &dbgregs,
+				 sizeof(struct kvm_debugregs)))
+			break;
+		r = 0;
+		break;
+	}
+	case KVM_SET_DEBUGREGS: {
+		struct kvm_debugregs dbgregs;
+
+		r = -EFAULT;
+		if (copy_from_user(&dbgregs, argp,
+				   sizeof(struct kvm_debugregs)))
+			break;
+
+		r = kvm_vcpu_ioctl_x86_set_debugregs(vcpu, &dbgregs);
+		break;
+	}
 	default:
 		r = -EINVAL;
 	}

include/linux/kvm.h

@@ -503,6 +503,9 @@ struct kvm_ioeventfd {
 #define KVM_CAP_PCI_SEGMENT 47
 #define KVM_CAP_PPC_PAIRED_SINGLES 48
 #define KVM_CAP_INTR_SHADOW 49
+#ifdef __KVM_HAVE_DEBUGREGS
+#define KVM_CAP_DEBUGREGS 50
+#endif
 #define KVM_CAP_X86_ROBUST_SINGLESTEP 51
 
 #ifdef KVM_CAP_IRQ_ROUTING
@@ -690,6 +693,9 @@ struct kvm_clock_data {
 /* Available with KVM_CAP_VCPU_EVENTS */
 #define KVM_GET_VCPU_EVENTS       _IOR(KVMIO,  0x9f, struct kvm_vcpu_events)
 #define KVM_SET_VCPU_EVENTS       _IOW(KVMIO,  0xa0, struct kvm_vcpu_events)
+/* Available with KVM_CAP_DEBUGREGS */
+#define KVM_GET_DEBUGREGS         _IOR(KVMIO,  0xa1, struct kvm_debugregs)
+#define KVM_SET_DEBUGREGS         _IOW(KVMIO,  0xa2, struct kvm_debugregs)
 
 #define KVM_DEV_ASSIGN_ENABLE_IOMMU	(1 << 0)