From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751773AbcFXPg5 (ORCPT ); Fri, 24 Jun 2016 11:36:57 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:41110 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751104AbcFXPgz (ORCPT ); Fri, 24 Jun 2016 11:36:55 -0400 X-IBM-Helo: d23dlp03.au.ibm.com X-IBM-MailFrom: xyjxie@linux.vnet.ibm.com X-IBM-RcptTo: kvm@vger.kernel.org;linux-kernel@vger.kernel.org Subject: Re: [PATCH v4] vfio-pci: Allow to mmap sub-page MMIO BARs if the mmio page is exclusive To: Alex Williamson References: <201605301311.u4UD99he028186@mx0a-001b2d01.pphosted.com> <20160623101245.78e3606b@t450s.home> <20160623213700.2ccfe903@t450s.home> Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, bhelgaas@google.com, aik@ozlabs.ru, benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au, warrier@linux.vnet.ibm.com, zhong@linux.vnet.ibm.com, nikunj@linux.vnet.ibm.com, gwshan@linux.vnet.ibm.com, kevin.tian@intel.com From: Yongji Xie Date: Fri, 24 Jun 2016 23:37:02 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 MIME-Version: 1.0 In-Reply-To: <20160623213700.2ccfe903@t450s.home> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16062415-0004-0000-0000-00000172B365 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16062415-0005-0000-0000-0000082483DA Message-Id: <3e0965bc-8c89-4534-6381-5af9469bbd7e@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-06-24_08:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1604210000 definitions=main-1606240168 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Alex On 2016/6/24 11:37, Alex Williamson wrote: > On Fri, 24 Jun 2016 10:52:58 +0800 > Yongji Xie wrote: >> On 2016/6/24 0:12, Alex Williamson wrote: >>> On Mon, 30 May 2016 21:06:37 +0800 >>> Yongji Xie wrote: >>>> +static void vfio_pci_probe_mmaps(struct vfio_pci_device *vdev) >>>> +{ >>>> + struct resource *res; >>>> + int bar; >>>> + struct vfio_pci_dummy_resource *dummy_res; >>>> + >>>> + INIT_LIST_HEAD(&vdev->dummy_resources_list); >>>> + >>>> + for (bar = PCI_STD_RESOURCES; bar <= PCI_STD_RESOURCE_END; bar++) { >>>> + res = vdev->pdev->resource + bar; >>>> + >>>> + if (!IS_ENABLED(CONFIG_VFIO_PCI_MMAP)) >>>> + goto no_mmap; >>>> + >>>> + if (!(res->flags & IORESOURCE_MEM)) >>>> + goto no_mmap; >>>> + >>>> + /* >>>> + * The PCI core shouldn't set up a resource with a >>>> + * type but zero size. But there may be bugs that >>>> + * cause us to do that. >>>> + */ >>>> + if (!resource_size(res)) >>>> + goto no_mmap; >>>> + >>>> + if (resource_size(res) >= PAGE_SIZE) { >>>> + vdev->bar_mmap_supported[bar] = true; >>>> + continue; >>>> + } >>>> + >>>> + if (!(res->start & ~PAGE_MASK)) { >>>> + /* >>>> + * Add a dummy resource to reserve the remainder >>>> + * of the exclusive page in case that hot-add >>>> + * device's bar is assigned into it. >>>> + */ >>>> + dummy_res = kzalloc(sizeof(*dummy_res), GFP_KERNEL); >>>> + if (dummy_res == NULL) >>>> + goto no_mmap; >>>> + >>>> + dummy_res->resource.start = res->end + 1; >>>> + dummy_res->resource.end = res->start + PAGE_SIZE - 1; >>>> + dummy_res->resource.flags = res->flags; >>>> + if (request_resource(res->parent, >>>> + &dummy_res->resource)) { >>>> + kfree(dummy_res); >>>> + goto no_mmap; >>>> + } >>> Isn't it true that request_resource() only tells us that at a given >>> point in time, no other drivers have reserved that resource? It seems >>> like it does not guarantee that the resource isn't routed to another >>> device or that another driver won't at some point attempt to request >>> that same resource. So for example if a user constructs their initrd >>> to bind vfio-pci to devices before other modules load, this >>> request_resource() may succeed, at the expense of drivers loaded later >>> now failing. The behavior will depend on driver load order and we're >>> not actually insuring that the overflow resource is unused, just that >>> we got it first. Can we do better? Am I missing something that >>> prevents this? Thanks, >>> >>> Alex >> Couldn't PCI resources allocator prevent this, which will find a >> empty slot in the resource tree firstly, then try to request that >> resource in allocate_resource() when a PCI device is probed. >> And I'd like to know why a PCI device driver would attempt to >> call request_resource()? Should this be done in PCI enumeration? > Hi Yongji, > > Looks like most pci drivers call pci_request_regions(). From there the > call path is: > > pci_request_selected_regions > __pci_request_selected_regions > __pci_request_region > __request_mem_region > __request_region > __request_resource > > We see this driver ordering issue sometimes with users attempting to > blacklist native pci drivers, trying to leave a device free for use by > vfio-pci. If the device is a graphics card, the generic vesa or uefi > driver can request device resources causing a failure when vfio-pci > tries to request those same resources. I expect that unless it's a > boot device, like vga in my example, the resources are not enabled > until the driver opens the device, therefore the request_resource() call > doesn't occur until that point. > > For another trivial example, look at /proc/iomem as you load and unload > a driver, on my laptop with e1000e unloaded I see: > > e1200000-e121ffff : 0000:00:19.0 > e123e000-e123efff : 0000:00:19.0 > > When e1000e is loaded, each of these becomes claimed by the e1000e > driver: > > e1200000-e121ffff : 0000:00:19.0 > e1200000-e121ffff : e1000e > e123e000-e123efff : 0000:00:19.0 > e123e000-e123efff : e1000e > > Clearly pci core knows the resource is associated with the device, but > I don't think we're tapping into that with request_resource(), we're > just potentially stealing resources that another driver might have > claimed otherwise as I described above. That's my suspicion at > least, feel free to show otherwise if it's incorrect. Thanks, > > Alex > Thanks for your explanation. But I still have one question. Shouldn't PCI core have claimed all PCI device's resources after probing those devices. If so, request_resource() will fail when vfio-pci try to steal resources that another driver might request later. Anything I missed here? Some device resources would not be claimed in PCI core? Thanks, Yongji