linux-kernel - [PATCH] KVM: x86: init x2apic

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Date:   Tue, 23 Jul 2019 21:06:08 +0800
From:   luferry@....com
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>
Cc:     "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        luferry <luferry@....com>
Subject: [PATCH] KVM: x86: init x2apic_enabled() once

From: luferry <luferry@....com>

x2apic_eanbled() costs about 200 cycles
when guest trigger halt pretty high, pi ops in hotpath

Signed-off-by: luferry <luferry@....com>
---
 arch/x86/kvm/vmx/vmx.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index d98eac371c0a..e17dbf011e47 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -186,6 +186,8 @@ static DEFINE_STATIC_KEY_FALSE(vmx_l1d_should_flush);
 static DEFINE_STATIC_KEY_FALSE(vmx_l1d_flush_cond);
 static DEFINE_MUTEX(vmx_l1d_flush_mutex);
 
+static int __read_mostly host_x2apic_enabled;
+
 /* Storage for pre module init parameter parsing */
 static enum vmx_l1d_flush_state __read_mostly vmentry_l1d_flush_param = VMENTER_L1D_FLUSH_AUTO;
 
@@ -1204,7 +1206,7 @@ static void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
 
 		dest = cpu_physical_id(cpu);
 
-		if (x2apic_enabled())
+		if (host_x2apic_enabled)
 			new.ndst = dest;
 		else
 			new.ndst = (dest << 8) & 0xFF00;
@@ -7151,7 +7153,7 @@ static void __pi_post_block(struct kvm_vcpu *vcpu)
 
 		dest = cpu_physical_id(vcpu->cpu);
 
-		if (x2apic_enabled())
+		if (host_x2apic_enabled)
 			new.ndst = dest;
 		else
 			new.ndst = (dest << 8) & 0xFF00;
@@ -7221,7 +7223,7 @@ static int pi_pre_block(struct kvm_vcpu *vcpu)
 		 */
 		dest = cpu_physical_id(vcpu->pre_pcpu);
 
-		if (x2apic_enabled())
+		if (host_x2apic_enabled)
 			new.ndst = dest;
 		else
 			new.ndst = (dest << 8) & 0xFF00;
@@ -7804,6 +7806,8 @@ static int __init vmx_init(void)
 	}
 #endif
 
+	host_x2apic_enabled = x2apic_enabled();
+
 	r = kvm_init(&vmx_x86_ops, sizeof(struct vcpu_vmx),
 		     __alignof__(struct vcpu_vmx), THIS_MODULE);
 	if (r)
-- 
2.14.1.40.g8e62ba1