[MODERATED] Re: [patch 15/15] SSB updates V17 15

[Paolo Bonzini <pbonzini@redhat.com>]

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On 17/05/2018 04:18, speck for Konrad Rzeszutek Wilk wrote:
>> @@ -4251,6 +4258,16 @@ static int svm_set_msr(struct kvm_vcpu *
>>  			break;
>>  		set_msr_interception(svm->msrpm, MSR_IA32_PRED_CMD, 0, 1);
>>  		break;
>> +	case MSR_AMD64_VIRT_SPEC_CTRL:
>> +		if (!msr->host_initiated &&
>> +		    !guest_cpuid_has(vcpu, X86_FEATURE_VIRT_SSBD))
>> +			return 1;
>> +
>> +		if (data & ~SPEC_CTRL_SSBD)
>> +			return 1;
>> +
>> +		svm->virt_spec_ctrl = data;
> 
> You need to save virt_spec_ctrl content for migration purposes.
> 
> It was introduced in "x86/bugs, KVM: Extend speculation control for VIRT_SPEC_CTRL"
> but not actually used so this patch is probably the best place to define it.
> 
> That is add this MSR in the 'msrs_to_save' or perhaps 'emulated_msrs'?

It's emulated_msrs since the MSR doesn't exist on bare metal.  But it also doesn't
exist on Intel, so:

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 949c977bc4c9..8a5d0fdb1d9a 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -924,7 +924,7 @@ struct kvm_x86_ops {
 	int (*hardware_setup)(void);               /* __init */
 	void (*hardware_unsetup)(void);            /* __exit */
 	bool (*cpu_has_accelerated_tpr)(void);
-	bool (*cpu_has_high_real_mode_segbase)(void);
+	bool (*has_emulated_msr)(int index);
 	void (*cpuid_update)(struct kvm_vcpu *vcpu);
 
 	struct kvm *(*vm_alloc)(void);
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index b58787daf9f8..5a2724c80ca6 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -5782,7 +5782,7 @@ static bool svm_cpu_has_accelerated_tpr(void)
 	return false;
 }
 
-static bool svm_has_high_real_mode_segbase(void)
+static bool svm_has_emulated_msr(int index)
 {
 	return true;
 }
@@ -7008,7 +7008,7 @@ static struct kvm_x86_ops svm_x86_ops __ro_after_init = {
 	.hardware_enable = svm_hardware_enable,
 	.hardware_disable = svm_hardware_disable,
 	.cpu_has_accelerated_tpr = svm_cpu_has_accelerated_tpr,
-	.cpu_has_high_real_mode_segbase = svm_has_high_real_mode_segbase,
+	.has_emulated_msr = svm_has_emulated_msr,
 
 	.vcpu_create = svm_create_vcpu,
 	.vcpu_free = svm_free_vcpu,
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index aafcc9881e88..ec1da2f44a75 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -9495,9 +9495,21 @@ static void vmx_handle_external_intr(struct kvm_vcpu *vcpu)
 }
 STACK_FRAME_NON_STANDARD(vmx_handle_external_intr);
 
-static bool vmx_has_high_real_mode_segbase(void)
+static bool vmx_has_emulated_msr(int index)
 {
-	return enable_unrestricted_guest || emulate_invalid_guest_state;
+	switch (index) {
+	case MSR_IA32_SMBASE:
+		/*
+		 * We cannot do SMM unless we can run the guest in big
+		 * real mode.
+		 */
+		return enable_unrestricted_guest || emulate_invalid_guest_state;
+	case MSR_AMD64_VIRT_SPEC_CTRL:
+		/* This is AMD only.  */
+		return false;
+	default:
+		return true;
+	}
 }
 
 static bool vmx_mpx_supported(void)
@@ -12622,7 +12634,7 @@ static struct kvm_x86_ops vmx_x86_ops __ro_after_init = {
 	.hardware_enable = hardware_enable,
 	.hardware_disable = hardware_disable,
 	.cpu_has_accelerated_tpr = report_flexpriority,
-	.cpu_has_high_real_mode_segbase = vmx_has_high_real_mode_segbase,
+	.has_emulated_msr = vmx_has_emulated_msr,
 
 	.vm_init = vmx_vm_init,
 	.vm_alloc = vmx_vm_alloc,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b2ff74b12ec4..6a9c640e7c4f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1058,6 +1058,7 @@ static u32 emulated_msrs[] = {
 	MSR_SMI_COUNT,
 	MSR_PLATFORM_INFO,
 	MSR_MISC_FEATURES_ENABLES,
+	MSR_AMD64_VIRT_SPEC_CTRL,
 };
 
 static unsigned num_emulated_msrs;
@@ -2894,7 +2895,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 		 * fringe case that is not enabled except via specific settings
 		 * of the module parameters.
 		 */
-		r = kvm_x86_ops->cpu_has_high_real_mode_segbase();
+		r = kvm_x86_ops->has_emulated_msr(MSR_IA32_SMBASE);
 		break;
 	case KVM_CAP_VAPIC:
 		r = !kvm_x86_ops->cpu_has_accelerated_tpr();
@@ -4594,14 +4595,8 @@ static void kvm_init_msr_list(void)
 	num_msrs_to_save = j;
 
 	for (i = j = 0; i < ARRAY_SIZE(emulated_msrs); i++) {
-		switch (emulated_msrs[i]) {
-		case MSR_IA32_SMBASE:
-			if (!kvm_x86_ops->cpu_has_high_real_mode_segbase())
-				continue;
-			break;
-		default:
-			break;
-		}
+		if (!kvm_x86_ops->has_emulated_msr(emulated_msrs[i]))
+			continue;
 
 		if (j < i)
 			emulated_msrs[j] = emulated_msrs[i];