From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1B4ADC4CEC4 for ; Mon, 23 Sep 2019 16:37:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ECAD72089F for ; Mon, 23 Sep 2019 16:37:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389238AbfIWQhr (ORCPT ); Mon, 23 Sep 2019 12:37:47 -0400 Received: from mga01.intel.com ([192.55.52.88]:60880 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389180AbfIWQhr (ORCPT ); Mon, 23 Sep 2019 12:37:47 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by fmsmga101.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 23 Sep 2019 09:37:47 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,541,1559545200"; d="scan'208";a="389536570" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.41]) by fmsmga006.fm.intel.com with ESMTP; 23 Sep 2019 09:37:46 -0700 Date: Mon, 23 Sep 2019 09:37:46 -0700 From: Sean Christopherson To: Vitaly Kuznetsov Cc: Andrea Arcangeli , Paolo Bonzini , "Dr. David Alan Gilbert" , Marcelo Tosatti , Peter Xu , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 15/17] KVM: retpolines: x86: eliminate retpoline from vmx.c exit handlers Message-ID: <20190923163746.GE18195@linux.intel.com> References: <20190920212509.2578-1-aarcange@redhat.com> <20190920212509.2578-16-aarcange@redhat.com> <87o8zb8ik1.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87o8zb8ik1.fsf@vitty.brq.redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Sep 23, 2019 at 11:31:58AM +0200, Vitaly Kuznetsov wrote: > Andrea Arcangeli writes: > > > It's enough to check the exit value and issue a direct call to avoid > > the retpoline for all the common vmexit reasons. > > > > Signed-off-by: Andrea Arcangeli > > --- > > arch/x86/kvm/vmx/vmx.c | 24 ++++++++++++++++++++++-- > > 1 file changed, 22 insertions(+), 2 deletions(-) > > > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > > index a6e597025011..9aa73e216df2 100644 > > --- a/arch/x86/kvm/vmx/vmx.c > > +++ b/arch/x86/kvm/vmx/vmx.c > > @@ -5866,9 +5866,29 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu) > > } > > > > if (exit_reason < kvm_vmx_max_exit_handlers > > - && kvm_vmx_exit_handlers[exit_reason]) > > + && kvm_vmx_exit_handlers[exit_reason]) { > > +#ifdef CONFIG_RETPOLINE > > + if (exit_reason == EXIT_REASON_MSR_WRITE) > > + return handle_wrmsr(vcpu); > > + else if (exit_reason == EXIT_REASON_PREEMPTION_TIMER) > > + return handle_preemption_timer(vcpu); > > + else if (exit_reason == EXIT_REASON_PENDING_INTERRUPT) > > + return handle_interrupt_window(vcpu); > > + else if (exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT) > > + return handle_external_interrupt(vcpu); > > + else if (exit_reason == EXIT_REASON_HLT) > > + return handle_halt(vcpu); > > + else if (exit_reason == EXIT_REASON_PAUSE_INSTRUCTION) > > + return handle_pause(vcpu); > > + else if (exit_reason == EXIT_REASON_MSR_READ) > > + return handle_rdmsr(vcpu); > > + else if (exit_reason == EXIT_REASON_CPUID) > > + return handle_cpuid(vcpu); > > + else if (exit_reason == EXIT_REASON_EPT_MISCONFIG) > > + return handle_ept_misconfig(vcpu); > > +#endif > > return kvm_vmx_exit_handlers[exit_reason](vcpu); > > I agree with the identified set of most common vmexits, however, this > still looks a bit random. Would it be too much if we get rid of > kvm_vmx_exit_handlers completely replacing this code with one switch()? Hmm, that'd require redirects for nVMX functions since they are set at runtime. That isn't necessarily a bad thing. The approach could also be used if Paolo's idea of making kvm_vmx_max_exit_handlers const allows the compiler to avoid retpoline. E.g.: static int handle_vmx_instruction(struct kvm_vcpu *vcpu) { if (nested) return nested_vmx_handle_exit(vcpu); kvm_queue_exception(vcpu, UD_VECTOR); return 1; }