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=-0.8 required=3.0 tests=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 2D4A5C10F00 for ; Fri, 6 Mar 2020 07:57:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F0A882073D for ; Fri, 6 Mar 2020 07:57:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726047AbgCFH5X convert rfc822-to-8bit (ORCPT ); Fri, 6 Mar 2020 02:57:23 -0500 Received: from mga12.intel.com ([192.55.52.136]:45039 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725855AbgCFH5X (ORCPT ); Fri, 6 Mar 2020 02:57:23 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga106.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 05 Mar 2020 23:57:23 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,521,1574150400"; d="scan'208";a="275446946" Received: from fmsmsx103.amr.corp.intel.com ([10.18.124.201]) by fmsmga002.fm.intel.com with ESMTP; 05 Mar 2020 23:57:23 -0800 Received: from fmsmsx162.amr.corp.intel.com (10.18.125.71) by FMSMSX103.amr.corp.intel.com (10.18.124.201) with Microsoft SMTP Server (TLS) id 14.3.439.0; Thu, 5 Mar 2020 23:57:22 -0800 Received: from shsmsx151.ccr.corp.intel.com (10.239.6.50) by fmsmsx162.amr.corp.intel.com (10.18.125.71) with Microsoft SMTP Server (TLS) id 14.3.439.0; Thu, 5 Mar 2020 23:57:22 -0800 Received: from shsmsx104.ccr.corp.intel.com ([169.254.5.206]) by SHSMSX151.ccr.corp.intel.com ([169.254.3.201]) with mapi id 14.03.0439.000; Fri, 6 Mar 2020 15:57:19 +0800 From: "Tian, Kevin" To: Alex Williamson CC: "kvm@vger.kernel.org" , "linux-pci@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "dev@dpdk.org" , "mtosatti@redhat.com" , "thomas@monjalon.net" , "bluca@debian.org" , "jerinjacobk@gmail.com" , "Richardson, Bruce" , "cohuck@redhat.com" Subject: RE: [PATCH v2 5/7] vfio/pci: Add sriov_configure support Thread-Topic: [PATCH v2 5/7] vfio/pci: Add sriov_configure support Thread-Index: AQHV51YaoTnickP570etlLGInd5eAKgrQJIwgA6gtQCAAWITYA== Date: Fri, 6 Mar 2020 07:57:19 +0000 Message-ID: References: <158213716959.17090.8399427017403507114.stgit@gimli.home> <158213846731.17090.37693075723046377.stgit@gimli.home> <20200305112230.0dd77712@w520.home> In-Reply-To: <20200305112230.0dd77712@w520.home> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ctpclassification: CTP_NT x-titus-metadata-40: eyJDYXRlZ29yeUxhYmVscyI6IiIsIk1ldGFkYXRhIjp7Im5zIjoiaHR0cDpcL1wvd3d3LnRpdHVzLmNvbVwvbnNcL0ludGVsMyIsImlkIjoiMjY4MTQ2OWItZDU1Ny00ZGViLTk5ODEtODAzYjcxMDY3OWNhIiwicHJvcHMiOlt7Im4iOiJDVFBDbGFzc2lmaWNhdGlvbiIsInZhbHMiOlt7InZhbHVlIjoiQ1RQX05UIn1dfV19LCJTdWJqZWN0TGFiZWxzIjpbXSwiVE1DVmVyc2lvbiI6IjE3LjEwLjE4MDQuNDkiLCJUcnVzdGVkTGFiZWxIYXNoIjoiWEFkM0paSjhCUXhKS0JQdHFpWUw0NGhCOElseFk2c1daa3dnYjdwdUVJMzJJSHlIc3Y4MGxveFhmVDFVR0VVZCJ9 dlp-product: dlpe-windows dlp-version: 11.2.0.6 dlp-reaction: no-action x-originating-ip: [10.239.127.40] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > From: Alex Williamson > Sent: Friday, March 6, 2020 2:23 AM > > On Tue, 25 Feb 2020 03:08:00 +0000 > "Tian, Kevin" wrote: > > > > From: Alex Williamson > > > Sent: Thursday, February 20, 2020 2:54 AM > > > > > > With the VF Token interface we can now expect that a vfio userspace > > > driver must be in collaboration with the PF driver, an unwitting > > > userspace driver will not be able to get past the GET_DEVICE_FD step > > > in accessing the device. We can now move on to actually allowing > > > SR-IOV to be enabled by vfio-pci on the PF. Support for this is not > > > enabled by default in this commit, but it does provide a module option > > > for this to be enabled (enable_sriov=1). Enabling VFs is rather > > > straightforward, except we don't want to risk that a VF might get > > > autoprobed and bound to other drivers, so a bus notifier is used to > > > "capture" VFs to vfio-pci using the driver_override support. We > > > assume any later action to bind the device to other drivers is > > > condoned by the system admin and allow it with a log warning. > > > > > > vfio-pci will disable SR-IOV on a PF before releasing the device, > > > allowing a VF driver to be assured other drivers cannot take over the > > > PF and that any other userspace driver must know the shared VF token. > > > This support also does not provide a mechanism for the PF userspace > > > driver itself to manipulate SR-IOV through the vfio API. With this > > > patch SR-IOV can only be enabled via the host sysfs interface and the > > > PF driver user cannot create or remove VFs. > > > > I'm not sure how many devices can be properly configured simply > > with pci_enable_sriov. It is not unusual to require PF driver prepare > > something before turning PCI SR-IOV capability. If you look kernel > > PF drivers, there are only two using generic pci_sriov_configure_ > > simple (simple wrapper like pci_enable_sriov), while most others > > implementing their own callback. However vfio itself has no idea > > thus I'm not sure how an user knows whether using this option can > > actually meet his purpose. I may miss something here, possibly > > using DPDK as an example will make it clearer. > > There is still the entire vfio userspace driver interface. Imagine for > example that QEMU emulates the SR-IOV capability and makes a call out > to libvirt (or maybe runs with privs for the PF SR-IOV sysfs attribs) > when the guest enables SR-IOV. Can't we assume that any PF specific > support can still be performed in the userspace/guest driver, leaving > us with a very simple and generic sriov_configure callback in vfio-pci? Makes sense. One concern, though, is how an user could be warned if he inadvertently uses sysfs to enable SR-IOV on a vfio device whose userspace driver is incapable of handling it. Note any VFIO device, if SR-IOV capable, will allow user to do so once the module option is turned on and the callback is registered. I felt such uncertainty can be contained by toggling SR-IOV through a vfio api, but from your description obviously it is what you want to avoid. Is it due to the sequence reason, e.g. that SR-IOV must be enabled before userspace PF driver sets the token? Thanks Kevin