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 CBF70C17460 for ; Tue, 5 Nov 2019 14:11:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AA504204EC for ; Tue, 5 Nov 2019 14:11:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389529AbfKEOLw (ORCPT ); Tue, 5 Nov 2019 09:11:52 -0500 Received: from mx1.redhat.com ([209.132.183.28]:37606 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389484AbfKEOLw (ORCPT ); Tue, 5 Nov 2019 09:11:52 -0500 Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 745F180F6D for ; Tue, 5 Nov 2019 14:11:51 +0000 (UTC) Received: by mail-wr1-f72.google.com with SMTP id f16so12036745wrr.16 for ; Tue, 05 Nov 2019 06:11:51 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=EkDCY7ijO5SQqK949MOdQ62nUzWqq7wHG7AQeLvnhlw=; b=azpfQlqXRTHHXbFcMNB+kU6t0+Kz2e5LKrXMLUK/gBpsQD1jK10XVEwJ81BNpKzpwe pJKIHVqcDdm3w+/gRBiSvXDKOkcXgHxIHbMsDwFshlcTV9iYFMlHQiSmhdkArKL5B4w4 mI5P2aK+Mk2AsmsCUOFjojAzY/ROzlFv5Fo5X3oyBJeaGGPEGZPGD4SQZm1swtOZkO3c Vbizp5H3j/GvNf3OZAzt7+69I6LYwkgPHlmI+5XIq1TiTPIdDoTIU0smjIprVk3xUvZ9 p+JkuSMoKIJNMywBnZCKjENwIAdqJ+pBPyTQYVyttpMyoK3cIbmGh57zcugEHO8EAExL neYQ== X-Gm-Message-State: APjAAAUZV1GZ8GYAJDuFDS4dXFbLrrjlrg0XLWA5OQQ9DApdVKnw5cQk UEXBASon6sOsVbAV0EzShJwnaZnaNRIpfpLEZ6bTl6VayV5demtJKZNXqHNJybgak99c939nNuQ SHmfRhTcoy6ANiqv8WuUdKZrm X-Received: by 2002:adf:f192:: with SMTP id h18mr30049435wro.148.1572963110041; Tue, 05 Nov 2019 06:11:50 -0800 (PST) X-Google-Smtp-Source: APXvYqxUPTma9hOlEpDdUWQmQaJiZsL6tt3pXEjgbC4Z+qEmwG1hi7Kqk/a2UTfdviEV9OwuW0FLfA== X-Received: by 2002:adf:f192:: with SMTP id h18mr30049412wro.148.1572963109679; Tue, 05 Nov 2019 06:11:49 -0800 (PST) Received: from [192.168.10.150] ([93.56.166.5]) by smtp.gmail.com with ESMTPSA id q6sm21502159wrx.30.2019.11.05.06.11.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 05 Nov 2019 06:11:49 -0800 (PST) Subject: Re: [PATCH 03/13] kvm: monolithic: fixup x86-32 build To: Andrea Arcangeli Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Vitaly Kuznetsov , Sean Christopherson References: <20191104230001.27774-1-aarcange@redhat.com> <20191104230001.27774-4-aarcange@redhat.com> <6ed4a5cd-38b1-04f8-e3d5-3327a1bd5d87@redhat.com> <678358c1-0621-3d2a-186e-b60742b2a286@redhat.com> <20191105135414.GA30717@redhat.com> From: Paolo Bonzini Message-ID: <330acce5-a527-543b-84c0-f3d8d277a0e2@redhat.com> Date: Tue, 5 Nov 2019 15:09:37 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20191105135414.GA30717@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/11/19 14:54, Andrea Arcangeli wrote: > x86-64 is already bisectable. > > All other archs bisectable I didn't check them all anyway. > > Even 4/13 is suboptimal and needs to be re-done later in more optimal > way. I prefer all logic changes to happen at later steps so one can at > least bisect to something that functionally works like before. And > 4/13 also would need to be merged in the huge patch if one wants to > guarantee bisectability on all CPUs, but it'll just be hidden there in > the huge patch. > > Obviously I can squash both 3/13 and 4/13 into 2/13 but I don't feel > like doing the right thing by squashing them just to increase > bisectability. You can reorder patches so that kvm_x86_ops assignments never happen. That way, 4/13 for example would be moved to the very beginning. >> - look into how to remove the modpost warnings. A simple (though >> somewhat ugly) way is to keep a kvm.ko module that includes common >> virt/kvm/ code as well as, for x86 only, page_track.o. A few functions, >> such as kvm_mmu_gfn_disallow_lpage and kvm_mmu_gfn_allow_lpage, would >> have to be moved into mmu.h, but that's not a big deal. > > I think we should: > > 1) whitelist to shut off the warnings on demand Do you mean adding a whitelist to modpost? That would work, though I am not sure if the module maintainer (Jessica Yu) would accept that. > 2) verify that if two modules are registering the same export symbol > the second one fails to load and the module code is robust about > that, this hopefully should already be the case > > Provided verification of 2), the whitelist is more efficient than > losing 4k of ram in all KVM hypervisors out there. I agree. >> - provide at least some examples of replacing the NULL kvm_x86_ops >> checks with error codes in the function (or just early "return"s). I >> can help with the others, but remember that for the patch to be merged, >> kvm_x86_ops must be removed completely. > > Even if kvm_x86_ops wouldn't be guaranteed to go away, this would > already provide all the performance benefit to the KVM users, so I > wouldn't see a reason not to apply it even if kvm_x86_ops cannot go > away. The answer is maintainability. My suggestion is that we start looking into removing all assignments and tests of kvm_x86_ops, one step at a time. Until this is done, unfortunately we won't be able to reap the performance benefit. But the advantage is that this can be done in many separate submissions; it doesn't have to be one huge patch. Once this is done, removing kvm_x86_ops is trivial in the end. It's okay if the intermediate step has minimal performance regressions, we know what it will look like. I have to order patches with maintenance first and performance second, if possible. By the way, we are already planning to make some module parameters per-VM instead of global, so this refactoring would also help that effort. > Said that it will go away and there's no concern about it. It's > just that the patchset seems large enough already and it rejects > heavily already at every port. I simply stopped at the first self > contained step that provides all performance benefits. That is good enough to prove the feasibility of the idea, so I agree that was a good plan. Paolo > If I go ahead and remove kvm_x86_ops how do I know it won't reject > heavily the next day I rebase and I've to redo it all from scratch? If > you explain me how you're going to guarantee that I won't have to do > that work more than once I'd be happy to go ahead.