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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 072CEC2BA83 for ; Wed, 12 Feb 2020 16:22:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D1CFE2173E for ; Wed, 12 Feb 2020 16:22:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728639AbgBLQWW (ORCPT ); Wed, 12 Feb 2020 11:22:22 -0500 Received: from mga11.intel.com ([192.55.52.93]:17698 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727361AbgBLQWW (ORCPT ); Wed, 12 Feb 2020 11:22:22 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmsmga102.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 12 Feb 2020 08:22:21 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,433,1574150400"; d="scan'208";a="380807826" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by orsmga004.jf.intel.com with ESMTP; 12 Feb 2020 08:22:20 -0800 Date: Wed, 12 Feb 2020 08:22:20 -0800 From: Sean Christopherson To: Paolo Bonzini Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] KVM: x86/mmu: Avoid retpoline on ->page_fault() with TDP Message-ID: <20200212162220.GA15617@linux.intel.com> References: <20200206221434.23790-1-sean.j.christopherson@intel.com> <878sleg2z7.fsf@vitty.brq.redhat.com> <20200207155539.GC2401@linux.intel.com> <408bfd4c-7407-48cd-95fb-db44a7c1c2bf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <408bfd4c-7407-48cd-95fb-db44a7c1c2bf@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 Wed, Feb 12, 2020 at 12:55:09PM +0100, Paolo Bonzini wrote: > On 07/02/20 16:55, Sean Christopherson wrote: > > It becomes a matter of weighing the maintenance cost and robustness against > > the performance benefits. For the TDP case, amost no one (that cares about > > performance) uses shadow paging, the change is very explicit, tiny and > > isolated, and TDP page fault are a hot path, e.g. when booting the VM. > > I.e. low maintenance overhead, still robust, and IMO worth the shenanigans. > > The "NULL" trick does not seem needed though. Any objections to this? Nope, no objections. > diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h > index 9277ee8a54a5..a647601c9e1c 100644 > --- a/arch/x86/kvm/mmu.h > +++ b/arch/x86/kvm/mmu.h > @@ -109,7 +109,7 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, > u32 err, bool prefault) > { > #ifdef CONFIG_RETPOLINE > - if (likely(!vcpu->arch.mmu->page_fault)) > + if (likely(vcpu->arch.mmu->page_fault == kvm_tdp_page_fault)) > return kvm_tdp_page_fault(vcpu, cr2_or_gpa, err, prefault); > #endif > return vcpu->arch.mmu->page_fault(vcpu, cr2_or_gpa, err, prefault); > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 5267f1440677..87e9ba27ada1 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -4925,12 +4925,7 @@ static void init_kvm_tdp_mmu(struct kvm_vcpu *vcpu) > return; > > context->mmu_role.as_u64 = new_role.as_u64; > -#ifdef CONFIG_RETPOLINE > - /* Nullify ->page_fault() to use direct kvm_tdp_page_fault() call. */ > - context->page_fault = NULL; > -#else > context->page_fault = kvm_tdp_page_fault; > -#endif > context->sync_page = nonpaging_sync_page; > context->invlpg = nonpaging_invlpg; > context->update_pte = nonpaging_update_pte; > > Paolo >