x86/KVM/VMX: Move the l1tf_flush_l1d test to vmx_l1d_flush()

Currently, vmx_vcpu_run() checks if l1tf_flush_l1d is set and invokes
vmx_l1d_flush() if so.

This test is unncessary for the "always flush L1D" mode.

Move the check to vmx_l1d_flush()'s conditional mode code path.

Notes:
- vmx_l1d_flush() is likely to get inlined anyway and thus, there's no
  extra function call.
  
- This inverts the (static) branch prediction, but there hadn't been any
  explicit likely()/unlikely() annotations before and so it stays as is.

Signed-off-by: Nicolai Stange <nstange@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kvm/vmx.c

@@ -9693,12 +9693,16 @@ static void vmx_l1d_flush(struct kvm_vcpu *vcpu)
 	 * 'always'
 	 */
 	if (static_branch_likely(&vmx_l1d_flush_cond)) {
+		bool flush_l1d = vcpu->arch.l1tf_flush_l1d;
+
 		/*
 		 * Clear the flush bit, it gets set again either from
 		 * vcpu_run() or from one of the unsafe VMEXIT
 		 * handlers.
 		 */
 		vcpu->arch.l1tf_flush_l1d = false;
+		if (!flush_l1d)
+			return;
 	}
 
 	vcpu->stat.l1d_flush++;
@@ -10228,10 +10232,8 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
 	evmcs_rsp = static_branch_unlikely(&enable_evmcs) ?
 		(unsigned long)&current_evmcs->host_rsp : 0;
 
-	if (static_branch_unlikely(&vmx_l1d_should_flush)) {
-		if (vcpu->arch.l1tf_flush_l1d)
+	if (static_branch_unlikely(&vmx_l1d_should_flush))
 		vmx_l1d_flush(vcpu);
-	}
 
 	asm(
 		/* Store host registers */