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@intel.com>
Message-Id: <20200410174703.1138-2-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 281436b..1fc10b8 100644 (file)
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6724,11 +6724,16 @@ 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;