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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 61607C43381 for ; Fri, 8 Mar 2019 02:21:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3C97C20675 for ; Fri, 8 Mar 2019 02:21:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726320AbfCHCVH (ORCPT ); Thu, 7 Mar 2019 21:21:07 -0500 Received: from mail-qt1-f194.google.com ([209.85.160.194]:40808 "EHLO mail-qt1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726242AbfCHCVH (ORCPT ); Thu, 7 Mar 2019 21:21:07 -0500 Received: by mail-qt1-f194.google.com with SMTP id f11so2402916qti.7 for ; Thu, 07 Mar 2019 18:21:06 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=2TXa20qb/Eg4W3WSZnBQT88vOwNyfmVbxryiRAAOMZ0=; b=WsRz4N5ulYZXHwgxcqwd+c0wjZYODsaqTqW4ZbACySREVZYM58p/X67TtBTzynBhSL 1YaWwtvopO/g8CXIHwfshhcIY4rOpwELxIgQgIjGPlwfPHosITceA7LdbSXjlB/gFo2f bONX0fiY+xdPoUPzIyleC9p3w7ridQqojMPmbP3I+T9sfIltoIxw0V4cZKQ9QyPtmi3/ QrggTuv9n+U4wcENu7mviwdXwvdwFPZpiUBjxW/E5n8GOVVN6hlk5kFhhH4i4nK6k9w0 vUmMuP9NSxOOlNayy2eX0xhGpEmizKgi3+8+BuyGvXwiPDERSHXF0jAlYy8Q75WQWVZz BHfA== X-Gm-Message-State: APjAAAWqTNQLi52l2MXm3R2z6jNEgVwBrC9/iv7OBZOvkN6Syp9t3clQ aXKrjEUQXNFPAmQwRRMtlkj0yw== X-Google-Smtp-Source: APXvYqzwmvqaJpBh6BkGPYK/AtjzjCuM+5N/KdCuho9+qlSH99IkjHAdDdmV+TJ2vuAvSfuxMvgJPA== X-Received: by 2002:a0c:a8d4:: with SMTP id h20mr13474604qvc.46.1552011666383; Thu, 07 Mar 2019 18:21:06 -0800 (PST) Received: from redhat.com (pool-173-76-246-42.bstnma.fios.verizon.net. [173.76.246.42]) by smtp.gmail.com with ESMTPSA id q57sm3931129qtj.79.2019.03.07.18.21.04 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 07 Mar 2019 18:21:05 -0800 (PST) Date: Thu, 7 Mar 2019 21:21:03 -0500 From: "Michael S. Tsirkin" To: Jerome Glisse Cc: Jason Wang , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, peterx@redhat.com, linux-mm@kvack.org, aarcange@redhat.com Subject: Re: [RFC PATCH V2 5/5] vhost: access vq metadata through kernel virtual address Message-ID: <20190307211506-mutt-send-email-mst@kernel.org> References: <1551856692-3384-1-git-send-email-jasowang@redhat.com> <1551856692-3384-6-git-send-email-jasowang@redhat.com> <20190307103503-mutt-send-email-mst@kernel.org> <20190307124700-mutt-send-email-mst@kernel.org> <20190307191720.GF3835@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190307191720.GF3835@redhat.com> Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Thu, Mar 07, 2019 at 02:17:20PM -0500, Jerome Glisse wrote: > > It's because of all these issues that I preferred just accessing > > userspace memory and handling faults. Unfortunately there does not > > appear to exist an API that whitelists a specific driver along the lines > > of "I checked this code for speculative info leaks, don't add barriers > > on data path please". > > Maybe it would be better to explore adding such helper then remapping > page into kernel address space ? I explored it a bit (see e.g. thread around: "__get_user slower than get_user") and I can tell you it's not trivial given the issue is around security. So in practice it does not seem fair to keep a significant optimization out of kernel because *maybe* we can do it differently even better :) -- MST