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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 82E4BC4725B for ; Tue, 5 May 2020 06:11:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 66A36206A5 for ; Tue, 5 May 2020 06:11:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728301AbgEEGLO (ORCPT ); Tue, 5 May 2020 02:11:14 -0400 Received: from mga03.intel.com ([134.134.136.65]:24371 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725320AbgEEGLO (ORCPT ); Tue, 5 May 2020 02:11:14 -0400 IronPort-SDR: 3GtEF5PyFJDPVq90cjqb9ep7/MHMuUWLkSzuqlYKj2Vcxkb/wn0exQH6QZK0Z200SQtUJJ0VW7 RMn1E3HLqa4Q== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 May 2020 23:11:08 -0700 IronPort-SDR: V7xGuKgTmHsrqJ1LWIleEXUUPdshBrPcR0pCTD8WwfbnMI/fV4SMleOaml1JQGO/MXh5MfGbj9 ZEjnYNeGfOTw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,354,1583222400"; d="scan'208";a="304386453" Received: from araj-mobl1.jf.intel.com ([10.254.74.162]) by FMSMGA003.fm.intel.com with ESMTP; 04 May 2020 23:11:07 -0700 Date: Mon, 4 May 2020 23:11:07 -0700 From: "Raj, Ashok" To: Alex Williamson Cc: linux-pci@vger.kernel.org, Bjorn Helgaas , linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, Lu Baolu , Darrel Goeddel , Mark Scott , Romil Sharma , Joerg Roedel , Ashok Raj Subject: Re: [PATCH] iommu: Relax ACS requirement for RCiEP devices. Message-ID: <20200505061107.GA22974@araj-mobl1.jf.intel.com> References: <1588653736-10835-1-git-send-email-ashok.raj@intel.com> <20200504231936.2bc07fe3@x1.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200504231936.2bc07fe3@x1.home> User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org Hi Alex + Joerg, accidently missed in the Cc. On Mon, May 04, 2020 at 11:19:36PM -0600, Alex Williamson wrote: > On Mon, 4 May 2020 21:42:16 -0700 > Ashok Raj wrote: > > > PCIe Spec recommends we can relax ACS requirement for RCIEP devices. > > > > PCIe 5.0 Specification. > > 6.12 Access Control Services (ACS) > > Implementation of ACS in RCiEPs is permitted but not required. It is > > explicitly permitted that, within a single Root Complex, some RCiEPs > > implement ACS and some do not. It is strongly recommended that Root Complex > > implementations ensure that all accesses originating from RCiEPs > > (PFs and VFs) without ACS capability are first subjected to processing by > > the Translation Agent (TA) in the Root Complex before further decoding and > > processing. The details of such Root Complex handling are outside the scope > > of this specification. > > > > Since Linux didn't give special treatment to allow this exception, certain > > RCiEP MFD devices are getting grouped in a single iommu group. This > > doesn't permit a single device to be assigned to a guest for instance. > > > > In one vendor system: Device 14.x were grouped in a single IOMMU group. > > > > /sys/kernel/iommu_groups/5/devices/0000:00:14.0 > > /sys/kernel/iommu_groups/5/devices/0000:00:14.2 > > /sys/kernel/iommu_groups/5/devices/0000:00:14.3 > > > > After the patch: > > /sys/kernel/iommu_groups/5/devices/0000:00:14.0 > > /sys/kernel/iommu_groups/5/devices/0000:00:14.2 > > /sys/kernel/iommu_groups/6/devices/0000:00:14.3 <<< new group > > > > 14.0 and 14.2 are integrated devices, but legacy end points. > > Whereas 14.3 was a PCIe compliant RCiEP. > > > > 00:14.3 Network controller: Intel Corporation Device 9df0 (rev 30) > > Capabilities: [40] Express (v2) Root Complex Integrated Endpoint, MSI 00 > > > > This permits assigning this device to a guest VM. > > > > Fixes: f096c061f552 ("iommu: Rework iommu_group_get_for_pci_dev()") > > Signed-off-by: Ashok Raj > > To: Joerg Roedel > > To: Bjorn Helgaas > > Cc: linux-kernel@vger.kernel.org > > Cc: iommu@lists.linux-foundation.org > > Cc: Lu Baolu > > Cc: Alex Williamson > > Cc: Darrel Goeddel > > Cc: Mark Scott , > > Cc: Romil Sharma > > Cc: Ashok Raj > > --- > > drivers/iommu/iommu.c | 15 ++++++++++++++- > > 1 file changed, 14 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c > > index 2b471419e26c..5744bd65f3e2 100644 > > --- a/drivers/iommu/iommu.c > > +++ b/drivers/iommu/iommu.c > > @@ -1187,7 +1187,20 @@ static struct iommu_group *get_pci_function_alias_group(struct pci_dev *pdev, > > struct pci_dev *tmp = NULL; > > struct iommu_group *group; > > > > - if (!pdev->multifunction || pci_acs_enabled(pdev, REQ_ACS_FLAGS)) > > + /* > > + * PCI Spec 5.0, Section 6.12 Access Control Service > > + * Implementation of ACS in RCiEPs is permitted but not required. > > + * It is explicitly permitted that, within a single Root > > + * Complex, some RCiEPs implement ACS and some do not. It is > > + * strongly recommended that Root Complex implementations ensure > > + * that all accesses originating from RCiEPs (PFs and VFs) without > > + * ACS capability are first subjected to processing by the Translation > > + * Agent (TA) in the Root Complex before further decoding and > > + * processing. > > + */ > > Is the language here really strong enough to make this change? ACS is > an optional feature, so being permitted but not required is rather > meaningless. The spec is also specifically avoiding the words "must" > or "shall" and even when emphasized with "strongly", we still only have > a recommendation that may or may not be honored. This seems like a > weak basis for assuming that RCiEPs universally honor this > recommendation. Thanks, > We are speaking about PCIe spec, where people write it about 5 years ahead and every vendor tries to massage their product behavior with vague words like this.. :) But honestly for any any RCiEP, or even integrated endpoints, there is no way to send them except up north. These aren't behind a RP. I did check with couple folks who are part of the SIG, and seem to agree that ACS treatment for RCiEP's doesn't mean much. I understand the language isn't strong, but it doesn't seem like ACS should be a strong requirement for RCiEP's and reasonable to relax. What are your thoughts? Cheers, Ashok > > > + if (!pdev->multifunction || > > + (pci_pcie_type(pdev) == PCI_EXP_TYPE_RC_END) || > > + pci_acs_enabled(pdev, REQ_ACS_FLAGS)) > > return NULL; > > > > for_each_pci_dev(tmp) { >