kvm: x86: Add emulation for IA32_XFD

Intel's eXtended Feature Disable (XFD) feature allows the software
to dynamically adjust fpstate buffer size for XSAVE features which
have large state.

Because guest fpstate has been expanded for all possible dynamic
xstates at KVM_SET_CPUID2, emulation of the IA32_XFD MSR is
straightforward. For write just call fpu_update_guest_xfd() to
update the guest fpu container once all the sanity checks are passed.
For read simply return the cached value in the container.
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Zeng Guang <guang.zeng@intel.com>
Signed-off-by: Wei Wang <wei.w.wang@intel.com>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Signed-off-by: Yang Zhong <yang.zhong@intel.com>
Message-Id: <20220105123532.12586-11-yang.zhong@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -1377,6 +1377,7 @@ static const u32 msrs_to_save_all[] = {
 	MSR_F15H_PERF_CTL3, MSR_F15H_PERF_CTL4, MSR_F15H_PERF_CTL5,
 	MSR_F15H_PERF_CTR0, MSR_F15H_PERF_CTR1, MSR_F15H_PERF_CTR2,
 	MSR_F15H_PERF_CTR3, MSR_F15H_PERF_CTR4, MSR_F15H_PERF_CTR5,
+	MSR_IA32_XFD,
 };
 
 static u32 msrs_to_save[ARRAY_SIZE(msrs_to_save_all)];
@@ -3686,6 +3687,19 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 			return 1;
 		vcpu->arch.msr_misc_features_enables = data;
 		break;
+#ifdef CONFIG_X86_64
+	case MSR_IA32_XFD:
+		if (!msr_info->host_initiated &&
+		    !guest_cpuid_has(vcpu, X86_FEATURE_XFD))
+			return 1;
+
+		if (data & ~(XFEATURE_MASK_USER_DYNAMIC &
+			     vcpu->arch.guest_supported_xcr0))
+			return 1;
+
+		fpu_update_guest_xfd(&vcpu->arch.guest_fpu, data);
+		break;
+#endif
 	default:
 		if (kvm_pmu_is_valid_msr(vcpu, msr))
 			return kvm_pmu_set_msr(vcpu, msr_info);
@@ -4006,6 +4020,15 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case MSR_K7_HWCR:
 		msr_info->data = vcpu->arch.msr_hwcr;
 		break;
+#ifdef CONFIG_X86_64
+	case MSR_IA32_XFD:
+		if (!msr_info->host_initiated &&
+		    !guest_cpuid_has(vcpu, X86_FEATURE_XFD))
+			return 1;
+
+		msr_info->data = vcpu->arch.guest_fpu.fpstate->xfd;
+		break;
+#endif
 	default:
 		if (kvm_pmu_is_valid_msr(vcpu, msr_info->index))
 			return kvm_pmu_get_msr(vcpu, msr_info);
@@ -6441,6 +6464,10 @@ static void kvm_init_msr_list(void)
 			    min(INTEL_PMC_MAX_GENERIC, x86_pmu.num_counters_gp))
 				continue;
 			break;
+		case MSR_IA32_XFD:
+			if (!kvm_cpu_cap_has(X86_FEATURE_XFD))
+				continue;
+			break;
 		default:
 			break;
 		}