KVM: VMX: read/write MSR_IA32_DEBUGCTLMSR from GUEST_IA32_DEBUGCTL

SVM already has specific handlers of MSR_IA32_DEBUGCTLMSR in the
svm_get/set_msr, so the x86 common part can be safely moved to VMX.
This allows KVM to store the bits it supports in GUEST_IA32_DEBUGCTL.

Add vmx_supported_debugctl() to refactor the throwing logic of #GP.

Signed-off-by: Like Xu <like.xu@linux.intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Message-Id: <20210108013704.134985-2-like.xu@linux.intel.com>
[Merge parts of Chenyi Qiang's "KVM: X86: Expose bus lock debug exception
 to guest". - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/capabilities.h

@@ -384,4 +384,9 @@ static inline u64 vmx_get_perf_capabilities(void)
 	return PMU_CAP_FW_WRITES;
 }
 
+static inline u64 vmx_supported_debugctl(void)
+{
+	return 0;
+}
+
 #endif /* __KVM_X86_VMX_CAPS_H */

arch/x86/kvm/vmx/vmx.c

@@ -1924,6 +1924,9 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		    !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
 			return 1;
 		goto find_uret_msr;
+	case MSR_IA32_DEBUGCTLMSR:
+		msr_info->data = vmcs_read64(GUEST_IA32_DEBUGCTL);
+		break;
 	default:
 	find_uret_msr:
 		msr = vmx_find_uret_msr(vmx, msr_info->index);
@@ -1997,14 +2000,26 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		}
 		vmcs_writel(GUEST_SYSENTER_ESP, data);
 		break;
-	case MSR_IA32_DEBUGCTLMSR:
+	case MSR_IA32_DEBUGCTLMSR: {
+		u64 invalid = data & ~vmx_supported_debugctl();
+		if (invalid & (DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR)) {
+			if (report_ignored_msrs)
+				vcpu_unimpl(vcpu, "%s: BTF|LBR in IA32_DEBUGCTLMSR 0x%llx, nop\n",
+					    __func__, data);
+			data &= ~(DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR);
+			invalid &= ~(DEBUGCTLMSR_BTF|DEBUGCTLMSR_LBR);
+		}
+
+		if (invalid)
+			return 1;
+
 		if (is_guest_mode(vcpu) && get_vmcs12(vcpu)->vm_exit_controls &
 						VM_EXIT_SAVE_DEBUG_CONTROLS)
 			get_vmcs12(vcpu)->guest_ia32_debugctl = data;
 
-		ret = kvm_set_msr_common(vcpu, msr_info);
-		break;
-
+		vmcs_write64(GUEST_IA32_DEBUGCTL, data);
+		return 0;
+	}
 	case MSR_IA32_BNDCFGS:
 		if (!kvm_mpx_supported() ||
 		    (!msr_info->host_initiated &&

arch/x86/kvm/x86.c

@@ -117,8 +117,9 @@ EXPORT_SYMBOL_GPL(kvm_x86_ops);
 static bool __read_mostly ignore_msrs = 0;
 module_param(ignore_msrs, bool, S_IRUGO | S_IWUSR);
 
-static bool __read_mostly report_ignored_msrs = true;
+bool __read_mostly report_ignored_msrs = true;
 module_param(report_ignored_msrs, bool, S_IRUGO | S_IWUSR);
+EXPORT_SYMBOL_GPL(report_ignored_msrs);
 
 unsigned int min_timer_period_us = 200;
 module_param(min_timer_period_us, uint, S_IRUGO | S_IWUSR);
@@ -3073,18 +3074,6 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 			return 1;
 		}
 		break;
-	case MSR_IA32_DEBUGCTLMSR:
-		if (!data) {
-			/* We support the non-activated case already */
-			break;
-		} else if (data & ~(DEBUGCTLMSR_LBR | DEBUGCTLMSR_BTF)) {
-			/* Values other than LBR and BTF are vendor-specific,
-			   thus reserved and should throw a #GP */
-			return 1;
-		} else if (report_ignored_msrs)
-			vcpu_unimpl(vcpu, "%s: MSR_IA32_DEBUGCTLMSR 0x%llx, nop\n",
-				    __func__, data);
-		break;
 	case 0x200 ... 0x2ff:
 		return kvm_mtrr_set_msr(vcpu, msr, data);
 	case MSR_IA32_APICBASE:
@@ -3357,7 +3346,6 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	switch (msr_info->index) {
 	case MSR_IA32_PLATFORM_ID:
 	case MSR_IA32_EBL_CR_POWERON:
-	case MSR_IA32_DEBUGCTLMSR:
 	case MSR_IA32_LASTBRANCHFROMIP:
 	case MSR_IA32_LASTBRANCHTOIP:
 	case MSR_IA32_LASTINTFROMIP:

arch/x86/kvm/x86.h

@@ -296,6 +296,8 @@ extern int pi_inject_timer;
 
 extern struct static_key kvm_no_apic_vcpu;
 
+extern bool report_ignored_msrs;
+
 static inline u64 nsec_to_cycles(struct kvm_vcpu *vcpu, u64 nsec)
 {
 	return pvclock_scale_delta(nsec, vcpu->arch.virtual_tsc_mult,