KVM: x86: Update vCPU's runtime CPUID on write to MSR_IA32_XSS

Do a runtime CPUID update for a vCPU if MSR_IA32_XSS is written, as the
size in bytes of the XSAVE area is affected by the states enabled in XSS.

Fixes: 2030009 ("kvm: vmx: add MSR logic for XSAVES")
Cc: [email protected]
Signed-off-by: Like Xu <[email protected]>
[sean: split out as a separate patch, adjust Fixes tag]
Signed-off-by: Sean Christopherson <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

Author: Like Xu

arch/x86/kvm/x86.c

@@ -3535,6 +3535,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		if (data & ~supported_xss)
 			return 1;
 		vcpu->arch.ia32_xss = data;
+		kvm_update_cpuid_runtime(vcpu);
 		break;
 	case MSR_SMI_COUNT:
 		if (!msr_info->host_initiated)