[patch V10 05/10] Control knobs and Documentation 5

[Thomas Gleixner <tglx@linutronix.de>]

Subject: [patch V10 05/10] x86/kvm: Add static key for flush always
From: Thomas Gleixner <tglx@linutronix.de>

Avoid the conditional in the L1D flush control path.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/kvm/vmx.c |   16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -192,6 +192,7 @@ module_param(ple_window_max, uint, 0444)
 extern const ulong vmx_return;
 
 static DEFINE_STATIC_KEY_FALSE(vmx_l1d_should_flush);
+static DEFINE_STATIC_KEY_FALSE(vmx_l1d_flush_always);
 
 /* Storage for pre module init parameter parsing */
 static enum vmx_l1d_flush_state __read_mostly vmentry_l1d_flush_param = VMENTER_L1D_FLUSH_AUTO;
@@ -232,8 +233,12 @@ static int vmx_setup_l1d_flush(enum vmx_
 
 	l1tf_vmx_mitigation = l1tf;
 
-	if (l1tf != VMENTER_L1D_FLUSH_NEVER)
-		static_branch_enable(&vmx_l1d_should_flush);
+	if (l1tf == VMENTER_L1D_FLUSH_NEVER)
+		return 0;
+
+	static_branch_enable(&vmx_l1d_should_flush);
+	if (l1tf == VMENTER_L1D_FLUSH_ALWAYS)
+		static_branch_enable(&vmx_l1d_flush_always);
 	return 0;
 }
 
@@ -9651,7 +9656,6 @@ static void *vmx_l1d_flush_pages;
 static void vmx_l1d_flush(struct kvm_vcpu *vcpu)
 {
 	int size = PAGE_SIZE << L1D_CACHE_ORDER;
-	bool always;
 
 	/*
 	 * This code is only executed when the the flush mode is 'cond' or
@@ -9661,8 +9665,10 @@ static void vmx_l1d_flush(struct kvm_vcp
 	 * it. The flush bit gets set again either from vcpu_run() or from
 	 * one of the unsafe VMEXIT handlers.
 	 */
-	always = l1tf_vmx_mitigation == VMENTER_L1D_FLUSH_ALWAYS;
-	vcpu->arch.l1tf_flush_l1d = always;
+	if (static_branch_unlikely(&vmx_l1d_flush_always))
+		vcpu->arch.l1tf_flush_l1d = true;
+	else
+		vcpu->arch.l1tf_flush_l1d = false;
 
 	vcpu->stat.l1d_flush++;