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=-4.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, 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 6A29AC433E0 for ; Fri, 17 Jul 2020 09:09:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 41BD8206F4 for ; Fri, 17 Jul 2020 09:09:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="LaZvUjdg" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726550AbgGQJJP (ORCPT ); Fri, 17 Jul 2020 05:09:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51062 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726037AbgGQJJO (ORCPT ); Fri, 17 Jul 2020 05:09:14 -0400 Received: from mail-ed1-x544.google.com (mail-ed1-x544.google.com [IPv6:2a00:1450:4864:20::544]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9A4CDC061755 for ; Fri, 17 Jul 2020 02:09:14 -0700 (PDT) Received: by mail-ed1-x544.google.com with SMTP id by13so7086833edb.11 for ; Fri, 17 Jul 2020 02:09:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=5hAp7/Ut6hK4YsA1k2zD1LY3Swf7sq8YHylKSXCzPJI=; b=LaZvUjdgoZgnkJNplfexj1+VySl/Bvb12VUGBJbdN9LkSfjRY0gSDagxsUKxtavwl5 DSzVMGBRyg4xpS8GFJvxFhosd8bddV2YPKMkeXSIF8/E2ZAxdxxljL09VIJVYcRdKRgP gLHKv6Xq+V9ce7jucMxM8s30rLw8GUIGtJ3iNoDqb0HJ+0CsRkT4xp5/jBDYtGIweWBg Bwwqqhp11dQD2I4shX9GDTkA11VNRAjodljLnTCdSR7VYivTZbDljPpQ0sitVuAYUknO EnOYnw4D3KtJhh6Aw2JdVCN6eY7QaezKNk7xNcg5ioL2BvjOc6azurQ6eFwDhwv95ZrC 0QCg== 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=5hAp7/Ut6hK4YsA1k2zD1LY3Swf7sq8YHylKSXCzPJI=; b=B10oTwRNpipMYPxI3Mq/nyWN3zjTNBZOf4PkD2BLLGLv6LzVxtSqBWgT5ifFzCQBYh WVdZRqKQGVp3CxVtqVcHiD7omMX9+oqBIWc2Xo+ztPbMg8WzKqSKg+wdzoyGntGTs9QF E2nXnJm0f8Uod+wb9gYx8qBnsl2VhkWXUef1cqN8f3ODuT9Knf5XChclq3lnJbbBbl5v g2ZmbEbHzoMGZC3LtFV//C4GZ0I13e9tObaNtFlm3zxqKtHH6AWEog99RqGy0eWL9H8R b9Tp4pPQ2JLu8coe0BF4o6St9Vp0oQ7onj2/CXR+kBaBxEhYTAnTSc4YrBgx7anwujl9 q5cA== X-Gm-Message-State: AOAM530dDhKyzp7KnL8gYucZX4fNSauQM6wqfJvxeWv4bby3sn8Xo++T fHzdYOOZKjq48ElCyWJxqHq2lQ== X-Google-Smtp-Source: ABdhPJxujtV7hysPeFOIoqKwGlmSd8lfEd8PTxDutsJIVtdPPbK+E0Gu8GwztgA2bbvp1ZvOpUskzQ== X-Received: by 2002:a50:e8c8:: with SMTP id l8mr8512571edn.386.1594976953280; Fri, 17 Jul 2020 02:09:13 -0700 (PDT) Received: from myrica ([2001:1715:4e26:a7e0:116c:c27a:3e7f:5eaf]) by smtp.gmail.com with ESMTPSA id b14sm7271529ejg.18.2020.07.17.02.09.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 17 Jul 2020 02:09:12 -0700 (PDT) Date: Fri, 17 Jul 2020 11:09:00 +0200 From: Jean-Philippe Brucker To: Auger Eric Cc: "Liu, Yi L" , Will Deacon , "alex.williamson@redhat.com" , "baolu.lu@linux.intel.com" , "joro@8bytes.org" , "Tian, Kevin" , "jacob.jun.pan@linux.intel.com" , "Raj, Ashok" , "Tian, Jun J" , "Sun, Yi Y" , "peterx@redhat.com" , "Wu, Hao" , "stefanha@gmail.com" , "iommu@lists.linux-foundation.org" , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Robin Murphy Subject: Re: [PATCH v5 03/15] iommu/smmu: Report empty domain nesting info Message-ID: <20200717090900.GC4850@myrica> References: <1594552870-55687-1-git-send-email-yi.l.liu@intel.com> <1594552870-55687-4-git-send-email-yi.l.liu@intel.com> <20200713131454.GA2739@willie-the-truck> <20200716153959.GA447208@myrica> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, Jul 16, 2020 at 10:38:17PM +0200, Auger Eric wrote: > Hi Jean, > > On 7/16/20 5:39 PM, Jean-Philippe Brucker wrote: > > On Tue, Jul 14, 2020 at 10:12:49AM +0000, Liu, Yi L wrote: > >>> Have you verified that this doesn't break the existing usage of > >>> DOMAIN_ATTR_NESTING in drivers/vfio/vfio_iommu_type1.c? > >> > >> I didn't have ARM machine on my hand. But I contacted with Jean > >> Philippe, he confirmed no compiling issue. I didn't see any code > >> getting DOMAIN_ATTR_NESTING attr in current drivers/vfio/vfio_iommu_type1.c. > >> What I'm adding is to call iommu_domai_get_attr(, DOMAIN_ATTR_NESTIN) > >> and won't fail if the iommu_domai_get_attr() returns 0. This patch > >> returns an empty nesting info for DOMAIN_ATTR_NESTIN and return > >> value is 0 if no error. So I guess it won't fail nesting for ARM. > > > > I confirm that this series doesn't break the current support for > > VFIO_IOMMU_TYPE1_NESTING with an SMMUv3. That said... > > > > If the SMMU does not support stage-2 then there is a change in behavior > > (untested): after the domain is silently switched to stage-1 by the SMMU > > driver, VFIO will now query nesting info and obtain -ENODEV. Instead of > > succeding as before, the VFIO ioctl will now fail. I believe that's a fix > > rather than a regression, it should have been like this since the > > beginning. No known userspace has been using VFIO_IOMMU_TYPE1_NESTING so > > far, so I don't think it should be a concern. > But as Yi mentioned ealier, in the current vfio code there is no > DOMAIN_ATTR_NESTING query yet. That's why something that would have succeeded before will now fail: Before this series, if user asked for a VFIO_IOMMU_TYPE1_NESTING, it would have succeeded even if the SMMU didn't support stage-2, as the driver would have silently fallen back on stage-1 mappings (which work exactly the same as stage-2-only since there was no nesting supported). After the series, we do check for DOMAIN_ATTR_NESTING so if user asks for VFIO_IOMMU_TYPE1_NESTING and the SMMU doesn't support stage-2, the ioctl fails. I believe it's a good fix and completely harmless, but wanted to make sure no one objects because it's an ABI change. Thanks, Jean > In my SMMUV3 nested stage series, I added > such a query in vfio-pci.c to detect if I need to expose a fault region > but I already test both the returned value and the output arg. So to me > there is no issue with that change. > > > > And if userspace queries the nesting properties using the new ABI > > introduced in this patchset, it will obtain an empty struct. I think > > that's acceptable, but it may be better to avoid adding the nesting cap if > > @format is 0? > agreed > > Thanks > > Eric > > > > Thanks, > > Jean > > > >> > >> @Eric, how about your opinion? your dual-stage vSMMU support may > >> also share the vfio_iommu_type1.c code. > >> > >> Regards, > >> Yi Liu > >> > >>> Will > > >