kvm: x86: Disable RDMSR interception of IA32_XFD_ERR

This saves one unnecessary VM-exit in guest #NM handler, given that the
MSR is already restored with the guest value before the guest is resumed.
Suggested-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NJing Liu <jing2.liu@intel.com>
Signed-off-by: NYang Zhong <yang.zhong@intel.com>
Message-Id: <20220105123532.12586-15-yang.zhong@intel.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/vmx.c

@@ -162,6 +162,7 @@ static u32 vmx_possible_passthrough_msrs[MAX_POSSIBLE_PASSTHROUGH_MSRS] = {
 	MSR_FS_BASE,
 	MSR_GS_BASE,
 	MSR_KERNEL_GS_BASE,
+	MSR_IA32_XFD_ERR,
 #endif
 	MSR_IA32_SYSENTER_CS,
 	MSR_IA32_SYSENTER_ESP,
@@ -7288,6 +7289,11 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 		}
 	}
 
+	if (kvm_cpu_cap_has(X86_FEATURE_XFD))
+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_XFD_ERR, MSR_TYPE_R,
+					  !guest_cpuid_has(vcpu, X86_FEATURE_XFD));
+
+
 	set_cr4_guest_host_mask(vmx);
 
 	vmx_write_encls_bitmap(vcpu, NULL);

arch/x86/kvm/vmx/vmx.h

@@ -349,7 +349,7 @@ struct vcpu_vmx {
 	struct lbr_desc lbr_desc;
 
 	/* Save desired MSR intercept (read: pass-through) state */
-#define MAX_POSSIBLE_PASSTHROUGH_MSRS	13
+#define MAX_POSSIBLE_PASSTHROUGH_MSRS	14
 	struct {
 		DECLARE_BITMAP(read, MAX_POSSIBLE_PASSTHROUGH_MSRS);
 		DECLARE_BITMAP(write, MAX_POSSIBLE_PASSTHROUGH_MSRS);