linux-kernel - [PATCH 4.18 50/79] x86/kvm: Add static key for flush always

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Message-Id: <20180814171339.168012604@linuxfoundation.org>
Date:   Tue, 14 Aug 2018 19:17:09 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Jiri Kosina <jkosina@...e.cz>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: [PATCH 4.18 50/79] x86/kvm: Add static key for flush always

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Thomas Gleixner <tglx@...utronix.de>

Avoid the conditional in the L1D flush control path.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Jiri Kosina <jkosina@...e.cz>
Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@...hat.com>
Link: https://lkml.kernel.org/r/20180713142322.790914912@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 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;
 }
 
@@ -9687,7 +9692,6 @@ 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
@@ -9697,8 +9701,10 @@ 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++;