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=-2.4 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, USER_AGENT_MUTT autolearn=ham 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 2BE28C4646F for ; Sat, 4 Aug 2018 08:21:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C05B1217C5 for ; Sat, 4 Aug 2018 08:21:28 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="WSmdXWWl" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C05B1217C5 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726976AbeHDKVQ (ORCPT ); Sat, 4 Aug 2018 06:21:16 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:36630 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726055AbeHDKVQ (ORCPT ); Sat, 4 Aug 2018 06:21:16 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=Uml25wGYLkjpg9aNsn/Ka+LDmDT7cUM/OMuByV29RYs=; b=WSmdXWWlCIseVWNwwk0EUy3TC 2rN/5Qse9Yx3CNip1bdXJqTwrQfVlcm4CpEsA3mjHhMhhKUqk/LROlFAdFjDiBArBQ4siDRTpos3R qwwBOSg22EGPSATsDLHxyuLV1lWZWQ0XddHq3yvfWrMkL0DTRMbU7EgbmEqRFN+UISyM3nzb+5e3p rttChy9sthceXp63Z74xQqCX7Mj1dXc6c1shguLYwVgzkLE5El/zD4W+9LwWmu85f51s6x2z18y/y WOjTUIQtyn8mrgmgQE5Kq6JsVbdhSJeiml6F+Y5Vx3fUZm3mht7PtsSHsOWIrHR7yPbDVfWPdTHfH Q9MlvrQ1w==; Received: from hch by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1flroO-0003YB-Ig; Sat, 04 Aug 2018 08:21:20 +0000 Date: Sat, 4 Aug 2018 01:21:20 -0700 From: Christoph Hellwig To: Benjamin Herrenschmidt Cc: Christoph Hellwig , "Michael S. Tsirkin" , Will Deacon , Anshuman Khandual , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, aik@ozlabs.ru, robh@kernel.org, joe@perches.com, elfring@users.sourceforge.net, david@gibson.dropbear.id.au, jasowang@redhat.com, mpe@ellerman.id.au, linuxram@us.ibm.com, haren@linux.vnet.ibm.com, paulus@samba.org, srikar@linux.vnet.ibm.com, robin.murphy@arm.com, jean-philippe.brucker@arm.com, marc.zyngier@arm.com Subject: Re: [RFC 0/4] Virtio uses DMA API for all devices Message-ID: <20180804082120.GB4421@infradead.org> References: <20180802182959-mutt-send-email-mst@kernel.org> <82ccef6ec3d95ee43f3990a4a2d0aea87eb45e89.camel@kernel.crashing.org> <20180802200646-mutt-send-email-mst@kernel.org> <20180802225738-mutt-send-email-mst@kernel.org> <20180803070507.GA1344@infradead.org> <20180803160246.GA13794@infradead.org> <22310f58605169fe9de83abf78b59f593ff7fbb7.camel@kernel.crashing.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <22310f58605169fe9de83abf78b59f593ff7fbb7.camel@kernel.crashing.org> User-Agent: Mutt/1.9.2 (2017-12-15) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 03, 2018 at 01:58:46PM -0500, Benjamin Herrenschmidt wrote: > You are saying something along the lines of "I don't like an > instruction in your ISA, let's not support your entire CPU architecture > in Linux". No. I'm saying if you can't describe your architecture in the virtio spec document it is bogus. > Our setup is not fucked. It makes a LOT of sense and it's a very > sensible design. It's hitting a problem due to a corner case oddity in > virtio bypassing the MMU, we've worked around such corner cases many > times in the past without any problem, I fail to see what the problem > is here. No matter if you like it or not (I don't!) virtio is defined to bypass dma translations, it is very clearly stated in the spec. It has some ill-defined bits to bypass it, so if you want the dma mapping API to be used you'll have to set that bit (in its original form, a refined form, or an entirely newly defined sane form) and make sure your hypersivors always sets it. It's not rocket science, just a little bit for work to make sure your setup is actually going to work reliably and portably. > We aren't going to cancel years of HW and SW development for our Maybe you should have actually read the specs you are claiming to implemented before spending all that effort.