KVM: VMX: Introduce generic fastpath handler

Introduce generic fastpath handler to handle MSR fastpath, VMX-preemption
timer fastpath etc; move it after vmx_complete_interrupts() in order to
catch events delivered to the guest, and abort the fast path in later
patches.  While at it, move the kvm_exit tracepoint so that it is printed
for fastpath vmexits as well.

There is no observed performance effect for the IPI fastpath after this patch.
Tested-by: Haiwei Li <lihaiwei@tencent.com>
Cc: Haiwei Li <lihaiwei@tencent.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Suggested-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <1588055009-12677-2-git-send-email-wanpengli@tencent.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/vmx.c

@@ -5933,8 +5933,6 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu,
 	u32 exit_reason = vmx->exit_reason;
 	u32 vectoring_info = vmx->idt_vectoring_info;
 
-	trace_kvm_exit(exit_reason, vcpu, KVM_ISA_VMX);
-
 	/*
 	 * Flush logged GPAs PML buffer, this will make dirty_bitmap more
 	 * updated. Another good is, in kvm_vm_ioctl_get_dirty_log, before
@@ -6630,6 +6628,16 @@ void vmx_update_host_rsp(struct vcpu_vmx *vmx, unsigned long host_rsp)
 	}
 }
 
+static enum exit_fastpath_completion vmx_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
+{
+	switch (to_vmx(vcpu)->exit_reason) {
+	case EXIT_REASON_MSR_WRITE:
+		return handle_fastpath_set_msr_irqoff(vcpu);
+	default:
+		return EXIT_FASTPATH_NONE;
+	}
+}
+
 bool __vmx_vcpu_run(struct vcpu_vmx *vmx, unsigned long *regs, bool launched);
 
 static enum exit_fastpath_completion vmx_vcpu_run(struct kvm_vcpu *vcpu)
@@ -6784,20 +6792,21 @@ static enum exit_fastpath_completion vmx_vcpu_run(struct kvm_vcpu *vcpu)
 	if (unlikely((u16)vmx->exit_reason == EXIT_REASON_MCE_DURING_VMENTRY))
 		kvm_machine_check();
 
+	trace_kvm_exit(vmx->exit_reason, vcpu, KVM_ISA_VMX);
+
 	if (unlikely(vmx->exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY))
 		return EXIT_FASTPATH_NONE;
 
-	if (!is_guest_mode(vcpu) && vmx->exit_reason == EXIT_REASON_MSR_WRITE)
-		exit_fastpath = handle_fastpath_set_msr_irqoff(vcpu);
-	else
-		exit_fastpath = EXIT_FASTPATH_NONE;
-
 	vmx->loaded_vmcs->launched = 1;
 	vmx->idt_vectoring_info = vmcs_read32(IDT_VECTORING_INFO_FIELD);
 
 	vmx_recover_nmi_blocking(vmx);
 	vmx_complete_interrupts(vmx);
 
+	if (is_guest_mode(vcpu))
+		return EXIT_FASTPATH_NONE;
+
+	exit_fastpath = vmx_exit_handlers_fastpath(vcpu);
 	return exit_fastpath;
 }