linux-kernel - [PATCH v3 1/2] KVM: VMX: Optimize handling of VM-Entry failures in vmx_vcpu

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Date:   Fri, 10 Apr 2020 10:47:02 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Haiwei Li <lihaiwei@...cent.com>
Subject: [PATCH v3 1/2] KVM: VMX: Optimize handling of VM-Entry failures in vmx_vcpu_run()

Mark the VM-Fail, VM-Exit on VM-Enter, and #MC on VM-Enter paths as
'unlikely' so as to improve code generation so that it favors successful
VM-Enter.  The performance of successful VM-Enter is for more important,
irrespective of whether or not success is actually likely.

Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/vmx/vmx.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 1d2bb57f4ac4..a8402bed29e3 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6736,11 +6736,16 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
 	vmx->nested.nested_run_pending = 0;
 	vmx->idt_vectoring_info = 0;
 
-	vmx->exit_reason = vmx->fail ? 0xdead : vmcs_read32(VM_EXIT_REASON);
-	if ((u16)vmx->exit_reason == EXIT_REASON_MCE_DURING_VMENTRY)
+	if (unlikely(vmx->fail)) {
+		vmx->exit_reason = 0xdead;
+		return;
+	}
+
+	vmx->exit_reason = vmcs_read32(VM_EXIT_REASON);
+	if (unlikely((u16)vmx->exit_reason == EXIT_REASON_MCE_DURING_VMENTRY))
 		kvm_machine_check();
 
-	if (vmx->fail || (vmx->exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY))
+	if (unlikely(vmx->exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY))
 		return;
 
 	vmx->loaded_vmcs->launched = 1;
-- 
2.26.0