[PATCH v3 1/2] KVM: VMX: Optimize handling of VM-Entry failures in vmx_vcpu_run()

From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Haiwei Li <lihaiwei@tencent.com>
Subject: [PATCH v3 1/2] KVM: VMX: Optimize handling of VM-Entry failures in vmx_vcpu_run()
Date: Fri, 10 Apr 2020 10:47:02 -0700	[thread overview]
Message-ID: <20200410174703.1138-2-sean.j.christopherson@intel.com> (raw)
In-Reply-To: <20200410174703.1138-1-sean.j.christopherson@intel.com>

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@intel.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

