KVM: SVM: Fix reading of DR6

In contrast to VMX, SVM dose not automatically transfer DR6 into the
VCPU's arch.dr6. So if we face a DR6 read, we must consult a new vendor
hook to obtain the current value. And as SVM now picks the DR6 state
from its VMCB, we also need a set callback in order to write updates of
DR6 back.

Fixes a regression of 020df0794f.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -700,6 +700,8 @@ struct kvm_x86_ops {
 	void (*set_idt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);
 	void (*get_gdt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);
 	void (*set_gdt)(struct kvm_vcpu *vcpu, struct desc_ptr *dt);
+	u64 (*get_dr6)(struct kvm_vcpu *vcpu);
+	void (*set_dr6)(struct kvm_vcpu *vcpu, unsigned long value);
 	void (*set_dr7)(struct kvm_vcpu *vcpu, unsigned long value);
 	void (*cache_reg)(struct kvm_vcpu *vcpu, enum kvm_reg reg);
 	unsigned long (*get_rflags)(struct kvm_vcpu *vcpu);

arch/x86/kvm/svm.c

@@ -1671,6 +1671,19 @@ static void new_asid(struct vcpu_svm *svm, struct svm_cpu_data *sd)
 	mark_dirty(svm->vmcb, VMCB_ASID);
 }
 
+static u64 svm_get_dr6(struct kvm_vcpu *vcpu)
+{
+	return to_svm(vcpu)->vmcb->save.dr6;
+}
+
+static void svm_set_dr6(struct kvm_vcpu *vcpu, unsigned long value)
+{
+	struct vcpu_svm *svm = to_svm(vcpu);
+
+	svm->vmcb->save.dr6 = value;
+	mark_dirty(svm->vmcb, VMCB_DR);
+}
+
 static void svm_set_dr7(struct kvm_vcpu *vcpu, unsigned long value)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
@@ -4286,6 +4299,8 @@ static struct kvm_x86_ops svm_x86_ops = {
 	.set_idt = svm_set_idt,
 	.get_gdt = svm_get_gdt,
 	.set_gdt = svm_set_gdt,
+	.get_dr6 = svm_get_dr6,
+	.set_dr6 = svm_set_dr6,
 	.set_dr7 = svm_set_dr7,
 	.cache_reg = svm_cache_reg,
 	.get_rflags = svm_get_rflags,

arch/x86/kvm/vmx.c

@@ -5149,6 +5149,15 @@ static int handle_dr(struct kvm_vcpu *vcpu)
 	return 1;
 }
 
+static u64 vmx_get_dr6(struct kvm_vcpu *vcpu)
+{
+	return vcpu->arch.dr6;
+}
+
+static void vmx_set_dr6(struct kvm_vcpu *vcpu, unsigned long val)
+{
+}
+
 static void vmx_set_dr7(struct kvm_vcpu *vcpu, unsigned long val)
 {
 	vmcs_writel(GUEST_DR7, val);
@@ -8556,6 +8565,8 @@ static struct kvm_x86_ops vmx_x86_ops = {
 	.set_idt = vmx_set_idt,
 	.get_gdt = vmx_get_gdt,
 	.set_gdt = vmx_set_gdt,
+	.get_dr6 = vmx_get_dr6,
+	.set_dr6 = vmx_set_dr6,
 	.set_dr7 = vmx_set_dr7,
 	.cache_reg = vmx_cache_reg,
 	.get_rflags = vmx_get_rflags,

arch/x86/kvm/x86.c

@@ -722,6 +722,12 @@ unsigned long kvm_get_cr8(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(kvm_get_cr8);
 
+static void kvm_update_dr6(struct kvm_vcpu *vcpu)
+{
+	if (!(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP))
+		kvm_x86_ops->set_dr6(vcpu, vcpu->arch.dr6);
+}
+
 static void kvm_update_dr7(struct kvm_vcpu *vcpu)
 {
 	unsigned long dr7;
@@ -750,6 +756,7 @@ static int __kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val)
 		if (val & 0xffffffff00000000ULL)
 			return -1; /* #GP */
 		vcpu->arch.dr6 = (val & DR6_VOLATILE) | DR6_FIXED_1;
+		kvm_update_dr6(vcpu);
 		break;
 	case 5:
 		if (kvm_read_cr4_bits(vcpu, X86_CR4_DE))
@@ -791,7 +798,10 @@ static int _kvm_get_dr(struct kvm_vcpu *vcpu, int dr, unsigned long *val)
 			return 1;
 		/* fall through */
 	case 6:
-		*val = vcpu->arch.dr6;
+		if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP)
+			*val = vcpu->arch.dr6;
+		else
+			*val = kvm_x86_ops->get_dr6(vcpu);
 		break;
 	case 5:
 		if (kvm_read_cr4_bits(vcpu, X86_CR4_DE))
@@ -2960,8 +2970,11 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
 static void kvm_vcpu_ioctl_x86_get_debugregs(struct kvm_vcpu *vcpu,
 					     struct kvm_debugregs *dbgregs)
 {
+	unsigned long val;
+
 	memcpy(dbgregs->db, vcpu->arch.db, sizeof(vcpu->arch.db));
-	dbgregs->dr6 = vcpu->arch.dr6;
+	_kvm_get_dr(vcpu, 6, &val);
+	dbgregs->dr6 = val;
 	dbgregs->dr7 = vcpu->arch.dr7;
 	dbgregs->flags = 0;
 	memset(&dbgregs->reserved, 0, sizeof(dbgregs->reserved));
@@ -2975,6 +2988,7 @@ static int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu,
 
 	memcpy(vcpu->arch.db, dbgregs->db, sizeof(vcpu->arch.db));
 	vcpu->arch.dr6 = dbgregs->dr6;
+	kvm_update_dr6(vcpu);
 	vcpu->arch.dr7 = dbgregs->dr7;
 	kvm_update_dr7(vcpu);
 
@@ -6749,6 +6763,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu)
 
 	memset(vcpu->arch.db, 0, sizeof(vcpu->arch.db));
 	vcpu->arch.dr6 = DR6_FIXED_1;
+	kvm_update_dr6(vcpu);
 	vcpu->arch.dr7 = DR7_FIXED_1;
 	kvm_update_dr7(vcpu);