KVM: SVM: enhance mov DR intercept handler

Newer SVM implementations provide the GPR number in the VMCB, so
that the emulation path is no longer necesarry to handle debug
register access intercepts. Implement the handling in svm.c and
use it when the info is provided.
Signed-off-by: Andre Przywara <andre.przywara@amd.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/kvm/svm.c

@@ -2745,6 +2745,30 @@ static int cr0_write_interception(struct vcpu_svm *svm)
 	return r;
 }
 
+static int dr_interception(struct vcpu_svm *svm)
+{
+	int reg, dr;
+	unsigned long val;
+	int err;
+
+	if (!boot_cpu_has(X86_FEATURE_DECODEASSISTS))
+		return emulate_on_interception(svm);
+
+	reg = svm->vmcb->control.exit_info_1 & SVM_EXITINFO_REG_MASK;
+	dr = svm->vmcb->control.exit_code - SVM_EXIT_READ_DR0;
+
+	if (dr >= 16) { /* mov to DRn */
+		val = kvm_register_read(&svm->vcpu, reg);
+		kvm_set_dr(&svm->vcpu, dr - 16, val);
+	} else {
+		err = kvm_get_dr(&svm->vcpu, dr, &val);
+		if (!err)
+			kvm_register_write(&svm->vcpu, reg, val);
+	}
+
+	return 1;
+}
+
 static int cr8_write_interception(struct vcpu_svm *svm)
 {
 	struct kvm_run *kvm_run = svm->vcpu.run;
@@ -3010,22 +3034,22 @@ static int (*svm_exit_handlers[])(struct vcpu_svm *svm) = {
 	[SVM_EXIT_WRITE_CR3]			= cr_interception,
 	[SVM_EXIT_WRITE_CR4]			= cr_interception,
 	[SVM_EXIT_WRITE_CR8]			= cr8_write_interception,
-	[SVM_EXIT_READ_DR0]			= emulate_on_interception,
-	[SVM_EXIT_READ_DR1]			= emulate_on_interception,
-	[SVM_EXIT_READ_DR2]			= emulate_on_interception,
-	[SVM_EXIT_READ_DR3]			= emulate_on_interception,
-	[SVM_EXIT_READ_DR4]			= emulate_on_interception,
-	[SVM_EXIT_READ_DR5]			= emulate_on_interception,
-	[SVM_EXIT_READ_DR6]			= emulate_on_interception,
-	[SVM_EXIT_READ_DR7]			= emulate_on_interception,
-	[SVM_EXIT_WRITE_DR0]			= emulate_on_interception,
-	[SVM_EXIT_WRITE_DR1]			= emulate_on_interception,
-	[SVM_EXIT_WRITE_DR2]			= emulate_on_interception,
-	[SVM_EXIT_WRITE_DR3]			= emulate_on_interception,
-	[SVM_EXIT_WRITE_DR4]			= emulate_on_interception,
-	[SVM_EXIT_WRITE_DR5]			= emulate_on_interception,
-	[SVM_EXIT_WRITE_DR6]			= emulate_on_interception,
-	[SVM_EXIT_WRITE_DR7]			= emulate_on_interception,
+	[SVM_EXIT_READ_DR0]			= dr_interception,
+	[SVM_EXIT_READ_DR1]			= dr_interception,
+	[SVM_EXIT_READ_DR2]			= dr_interception,
+	[SVM_EXIT_READ_DR3]			= dr_interception,
+	[SVM_EXIT_READ_DR4]			= dr_interception,
+	[SVM_EXIT_READ_DR5]			= dr_interception,
+	[SVM_EXIT_READ_DR6]			= dr_interception,
+	[SVM_EXIT_READ_DR7]			= dr_interception,
+	[SVM_EXIT_WRITE_DR0]			= dr_interception,
+	[SVM_EXIT_WRITE_DR1]			= dr_interception,
+	[SVM_EXIT_WRITE_DR2]			= dr_interception,
+	[SVM_EXIT_WRITE_DR3]			= dr_interception,
+	[SVM_EXIT_WRITE_DR4]			= dr_interception,
+	[SVM_EXIT_WRITE_DR5]			= dr_interception,
+	[SVM_EXIT_WRITE_DR6]			= dr_interception,
+	[SVM_EXIT_WRITE_DR7]			= dr_interception,
 	[SVM_EXIT_EXCP_BASE + DB_VECTOR]	= db_interception,
 	[SVM_EXIT_EXCP_BASE + BP_VECTOR]	= bp_interception,
 	[SVM_EXIT_EXCP_BASE + UD_VECTOR]	= ud_interception,