KVM: SVM: enhance MOV CR intercept handler

Newer SVM implementations provide the GPR number in the VMCB, so
that the emulation path is no longer necesarry to handle CR
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/include/asm/svm.h

@@ -260,6 +260,8 @@ struct __attribute__ ((__packed__)) vmcb {
 #define SVM_EXITINFOSHIFT_TS_REASON_JMP 38
 #define SVM_EXITINFOSHIFT_TS_HAS_ERROR_CODE 44
 
+#define SVM_EXITINFO_REG_MASK 0x0F
+
 #define	SVM_EXIT_READ_CR0 	0x000
 #define	SVM_EXIT_READ_CR3 	0x003
 #define	SVM_EXIT_READ_CR4 	0x004

arch/x86/kvm/svm.c

@@ -2660,12 +2660,80 @@ static int emulate_on_interception(struct vcpu_svm *svm)
 	return emulate_instruction(&svm->vcpu, 0) == EMULATE_DONE;
 }
 
+#define CR_VALID (1ULL << 63)
+
+static int cr_interception(struct vcpu_svm *svm)
+{
+	int reg, cr;
+	unsigned long val;
+	int err;
+
+	if (!static_cpu_has(X86_FEATURE_DECODEASSISTS))
+		return emulate_on_interception(svm);
+
+	if (unlikely((svm->vmcb->control.exit_info_1 & CR_VALID) == 0))
+		return emulate_on_interception(svm);
+
+	reg = svm->vmcb->control.exit_info_1 & SVM_EXITINFO_REG_MASK;
+	cr = svm->vmcb->control.exit_code - SVM_EXIT_READ_CR0;
+
+	err = 0;
+	if (cr >= 16) { /* mov to cr */
+		cr -= 16;
+		val = kvm_register_read(&svm->vcpu, reg);
+		switch (cr) {
+		case 0:
+			err = kvm_set_cr0(&svm->vcpu, val);
+			break;
+		case 3:
+			err = kvm_set_cr3(&svm->vcpu, val);
+			break;
+		case 4:
+			err = kvm_set_cr4(&svm->vcpu, val);
+			break;
+		case 8:
+			err = kvm_set_cr8(&svm->vcpu, val);
+			break;
+		default:
+			WARN(1, "unhandled write to CR%d", cr);
+			kvm_queue_exception(&svm->vcpu, UD_VECTOR);
+			return 1;
+		}
+	} else { /* mov from cr */
+		switch (cr) {
+		case 0:
+			val = kvm_read_cr0(&svm->vcpu);
+			break;
+		case 2:
+			val = svm->vcpu.arch.cr2;
+			break;
+		case 3:
+			val = svm->vcpu.arch.cr3;
+			break;
+		case 4:
+			val = kvm_read_cr4(&svm->vcpu);
+			break;
+		case 8:
+			val = kvm_get_cr8(&svm->vcpu);
+			break;
+		default:
+			WARN(1, "unhandled read from CR%d", cr);
+			kvm_queue_exception(&svm->vcpu, UD_VECTOR);
+			return 1;
+		}
+		kvm_register_write(&svm->vcpu, reg, val);
+	}
+	kvm_complete_insn_gp(&svm->vcpu, err);
+
+	return 1;
+}
+
 static int cr0_write_interception(struct vcpu_svm *svm)
 {
 	struct kvm_vcpu *vcpu = &svm->vcpu;
 	int r;
 
-	r = emulate_instruction(&svm->vcpu, 0);
+	r = cr_interception(svm);
 
 	if (svm->nested.vmexit_rip) {
 		kvm_register_write(vcpu, VCPU_REGS_RIP, svm->nested.vmexit_rip);
@@ -2674,7 +2742,7 @@ static int cr0_write_interception(struct vcpu_svm *svm)
 		svm->nested.vmexit_rip = 0;
 	}
 
-	return r == EMULATE_DONE;
+	return r;
 }
 
 static int cr8_write_interception(struct vcpu_svm *svm)
@@ -2684,13 +2752,13 @@ static int cr8_write_interception(struct vcpu_svm *svm)
 
 	u8 cr8_prev = kvm_get_cr8(&svm->vcpu);
 	/* instruction emulation calls kvm_set_cr8() */
-	r = emulate_instruction(&svm->vcpu, 0);
+	r = cr_interception(svm);
 	if (irqchip_in_kernel(svm->vcpu.kvm)) {
 		clr_cr_intercept(svm, INTERCEPT_CR8_WRITE);
-		return r == EMULATE_DONE;
+		return r;
 	}
 	if (cr8_prev <= kvm_get_cr8(&svm->vcpu))
-		return r == EMULATE_DONE;
+		return r;
 	kvm_run->exit_reason = KVM_EXIT_SET_TPR;
 	return 0;
 }
@@ -2933,14 +3001,14 @@ static int pause_interception(struct vcpu_svm *svm)
 }
 
 static int (*svm_exit_handlers[])(struct vcpu_svm *svm) = {
-	[SVM_EXIT_READ_CR0]			= emulate_on_interception,
-	[SVM_EXIT_READ_CR3]			= emulate_on_interception,
-	[SVM_EXIT_READ_CR4]			= emulate_on_interception,
-	[SVM_EXIT_READ_CR8]			= emulate_on_interception,
+	[SVM_EXIT_READ_CR0]			= cr_interception,
+	[SVM_EXIT_READ_CR3]			= cr_interception,
+	[SVM_EXIT_READ_CR4]			= cr_interception,
+	[SVM_EXIT_READ_CR8]			= cr_interception,
 	[SVM_EXIT_CR0_SEL_WRITE]		= emulate_on_interception,
 	[SVM_EXIT_WRITE_CR0]			= cr0_write_interception,
-	[SVM_EXIT_WRITE_CR3]			= emulate_on_interception,
-	[SVM_EXIT_WRITE_CR4]			= emulate_on_interception,
+	[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,