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=-3.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS 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 D35E5C3F2D1 for ; Mon, 2 Mar 2020 09:28:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AA439246B9 for ; Mon, 2 Mar 2020 09:28:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="sH6kyBtD" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727502AbgCBJ2S (ORCPT ); Mon, 2 Mar 2020 04:28:18 -0500 Received: from mail-pj1-f66.google.com ([209.85.216.66]:37195 "EHLO mail-pj1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726887AbgCBJ2N (ORCPT ); Mon, 2 Mar 2020 04:28:13 -0500 Received: by mail-pj1-f66.google.com with SMTP id o2so2262759pjp.2; Mon, 02 Mar 2020 01:28:12 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=PY4MuK9MtCzBBPb4BM+bF8sugRCFY9M8l8A3pQbpdiw=; b=sH6kyBtDw0rtBL8JJCp0gjcaIXkgXwiRFurf3c/d+4vPM+9vWt287P81nKtqzYG0ay 5LF5ZvgufuVwc0sxB/FUyX4E8LUUFoOAqBgsnezhD8RT/9n1Uzt/1xc1wYuUa7OaLjiJ lgvUFYzwNd0x0iY2+dE6EvBRCNCGQ6C2UUAxQAWhC5g251G7fQDxCdtCY1N+pkHQHt0O nRGLbt9L3RCF+nWlrzzqpG2CEphWVeLnwASyFQOQLELIObjMpjURtbGasFsETeQh9gxM TtVR69dovPrIrMvDbtFM2nyhKg3A2/j/5i6wGTahMAHbG0wgBl69tx4+TevNucn0A2kr yKrQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=PY4MuK9MtCzBBPb4BM+bF8sugRCFY9M8l8A3pQbpdiw=; b=n+/TvlhA9JEM2oGoRhrtIibXOmX2guZnA4cDYWb136V4KegQbgyaR1Z1IZSrmHNFh6 5YhAQHbjhmL+fpLrXPW7SaNLJ9Xlt4mnR4X5fP1Bnj5hBhfFiJp0KvsMV0sOoWafel6F pcUAQTYnLr0993L5EaM5mPrup+OmpqploxxlcFhJD0ukyuBZ8G1uf7Zh6WIGjpyKyr/y R8jkwQMtOkkgeCQemthVjC/IeOScXuyBEAq02iJuncUrkqmq/xuINs6BQZw/CW4eWMpW aRSt66CwYjgVTqlLZ71jbKrd83kaIONCVdzXHGTlP2eZxoHWbjMvWdYPXKngn1j2DGqR xQNw== X-Gm-Message-State: APjAAAUWJ64GhzqgurMOLoCeBK/PvDMj5SiLL119Yrq9y+ooFE6QbfOn CdNebKBKaC+PvQbNNw9wdvY= X-Google-Smtp-Source: APXvYqyeNNsZf2cgZjbOAIPSLGSZ+N52xHOXT7mNYakDKjVkVzamzuWHN7a0r80GFylvRLX8MXK76g== X-Received: by 2002:a17:90a:d101:: with SMTP id l1mr21047899pju.130.1583141292001; Mon, 02 Mar 2020 01:28:12 -0800 (PST) Received: from ?IPv6:2601:647:4700:9b2:999b:d09b:90a3:47d8? ([2601:647:4700:9b2:999b:d09b:90a3:47d8]) by smtp.gmail.com with ESMTPSA id x70sm11811963pgd.37.2020.03.02.01.28.08 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 02 Mar 2020 01:28:11 -0800 (PST) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 13.0 \(3608.60.0.2.5\)) Subject: Re: [PATCH v2] x86/kvm: Handle async page faults directly through do_page_fault() From: Nadav Amit In-Reply-To: <53626d08de5df34eacce80cb74f19a06fdc690c6.1582998497.git.luto@kernel.org> Date: Mon, 2 Mar 2020 01:28:04 -0800 Cc: LKML , x86 , kvm list , Paolo Bonzini Content-Transfer-Encoding: 7bit Message-Id: <34082A11-321D-4DF0-A076-7BBF332DCA66@gmail.com> References: <53626d08de5df34eacce80cb74f19a06fdc690c6.1582998497.git.luto@kernel.org> To: Andy Lutomirski X-Mailer: Apple Mail (2.3608.60.0.2.5) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Feb 29, 2020, at 9:50 AM, Andy Lutomirski wrote: > > KVM overloads #PF to indicate two types of not-actually-page-fault > events. Right now, the KVM guest code intercepts them by modifying > the IDT and hooking the #PF vector. This makes the already fragile > fault code even harder to understand, and it also pollutes call > traces with async_page_fault and do_async_page_fault for normal page > faults. > > Clean it up by moving the logic into do_page_fault() using a static > branch. This gets rid of the platform trap_init override mechanism > completely. > > Signed-off-by: Andy Lutomirski Indeed the async-PF mechanism is only used by KVM, and there is no need for over-engineering the solution just in case some other hypervisor ever introduces support for a similar paravirtual feature. Yet, this might be a slippery slope, making Linux optimized to run on KVM (and maybe Xen). In other words, I wonder whether a similar change was acceptable for a paravirtual feature that is only supported by a proprietary hypervisor, such as Hyper-V or VMware.