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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 91AACC00043 for ; Mon, 23 Sep 2019 21:08:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6CD8920665 for ; Mon, 23 Sep 2019 21:08:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388316AbfIWVIl (ORCPT ); Mon, 23 Sep 2019 17:08:41 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40104 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388040AbfIWVIl (ORCPT ); Mon, 23 Sep 2019 17:08:41 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 67CF530833A8; Mon, 23 Sep 2019 21:08:41 +0000 (UTC) Received: from mail (ovpn-120-159.rdu2.redhat.com [10.10.120.159]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A1FA65D71C; Mon, 23 Sep 2019 21:08:38 +0000 (UTC) Date: Mon, 23 Sep 2019 17:08:38 -0400 From: Andrea Arcangeli To: Sean Christopherson Cc: Paolo Bonzini , Vitaly Kuznetsov , "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: <20190923210838.GA23063@redhat.com> References: <20190920212509.2578-1-aarcange@redhat.com> <20190920212509.2578-16-aarcange@redhat.com> <87o8zb8ik1.fsf@vitty.brq.redhat.com> <7329012d-0b3b-ce86-f58d-3d2d5dc5a790@redhat.com> <20190923190514.GB19996@redhat.com> <20190923202349.GL18195@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190923202349.GL18195@linux.intel.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Mon, 23 Sep 2019 21:08:41 +0000 (UTC) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Hello, On Mon, Sep 23, 2019 at 01:23:49PM -0700, Sean Christopherson wrote: > The attached patch should do the trick. The two most attractive options to me remains what I already have implemented under #ifdef CONFIG_RETPOLINE with direct calls (optionally replacing the "if" with a small "switch" still under CONFIG_RETPOLINE if we give up the prioritization of the checks), or the replacement of kvm_vmx_exit_handlers with a switch() as suggested by Vitaly which would cleanup some code. The intermediate solution that makes "const" work, has the cons of forcing to parse EXIT_REASON_VMCLEAR and the other vmx exit reasons twice, first through a pointer to function (or another if or switch statement) then with a second switch() statement. If we'd use a single switch statement per Vitaly's suggestion, the "if nested" would better be more simply implemented as: switch (exit_reason) { case EXIT_REASON_VMCLEAR: if (nested) return handle_vmclear(vcpu); else return handle_vmx_instruction(vcpu); case EXIT_REASON_VMCLEAR: if (nested) [..] This also removes the compiler dependency to auto inline handle_vmclear in the added nested_vmx_handle_vmx_instruction extern call. VMREAD/WRITE/RESUME are the most frequent vmexit in l0 while nested runs in l2. Thanks, Andrea