KVM: VMX: Set VMENTER_L1D_FLUSH_NOT_REQUIRED if !X86_BUG_L1TF

The l1tf_vmx_mitigation is only set to VMENTER_L1D_FLUSH_NOT_REQUIRED
when the ARCH_CAPABILITIES MSR indicates that L1D flush is not required.
However, if the CPU is not affected by L1TF, l1tf_vmx_mitigation will
still be set to VMENTER_L1D_FLUSH_AUTO. This is certainly not the best
option for a !X86_BUG_L1TF CPU.

So force l1tf_vmx_mitigation to VMENTER_L1D_FLUSH_NOT_REQUIRED to make it
more explicit in case users are checking the vmentry_l1d_flush parameter.
Signed-off-by: Waiman Long <longman@redhat.com>
[Patch rewritten accoring to Borislav Petkov's suggestion. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/vmx.c

@@ -209,6 +209,11 @@ static int vmx_setup_l1d_flush(enum vmx_l1d_flush_state l1tf)
 	struct page *page;
 	unsigned int i;
 
+	if (!boot_cpu_has_bug(X86_BUG_L1TF)) {
+		l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_NOT_REQUIRED;
+		return 0;
+	}
+
 	if (!enable_ept) {
 		l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_EPT_DISABLED;
 		return 0;
@@ -7995,13 +8000,11 @@ static int __init vmx_init(void)
 	 * contain 'auto' which will be turned into the default 'cond'
 	 * mitigation mode.
 	 */
-	if (boot_cpu_has(X86_BUG_L1TF)) {
 	r = vmx_setup_l1d_flush(vmentry_l1d_flush_param);
 	if (r) {
 		vmx_exit();
 		return r;
 	}
-	}
 
 #ifdef CONFIG_KEXEC_CORE
 	rcu_assign_pointer(crash_vmclear_loaded_vmcss,