From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752220AbcGAGGX (ORCPT ); Fri, 1 Jul 2016 02:06:23 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:36539 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751932AbcGAGGS (ORCPT ); Fri, 1 Jul 2016 02:06:18 -0400 X-IBM-Helo: d23dlp03.au.ibm.com X-IBM-MailFrom: gwshan@linux.vnet.ibm.com X-IBM-RcptTo: linux-doc@vger.kernel.org;linux-kernel@vger.kernel.org;linux-pci@vger.kernel.org Date: Fri, 1 Jul 2016 16:05:19 +1000 From: Gavin Shan To: Yongji Xie Cc: Gavin Shan , nikunj@linux.vnet.ibm.com, zhong@linux.vnet.ibm.com, linux-doc@vger.kernel.org, aik@ozlabs.ru, linux-pci@vger.kernel.org, corbet@lwn.net, linux-kernel@vger.kernel.org, warrier@linux.vnet.ibm.com, alex.williamson@redhat.com, paulus@samba.org, bhelgaas@google.com, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH v3 2/7] PCI: Ignore enforced alignment to VF BARs Reply-To: Gavin Shan References: <1467283993-3185-1-git-send-email-xyjxie@linux.vnet.ibm.com> <1467283993-3185-3-git-send-email-xyjxie@linux.vnet.ibm.com> <20160701003959.GB15147@gwshan> <21112bd7-d343-46b6-1df1-b20cc1c1b24e@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <21112bd7-d343-46b6-1df1-b20cc1c1b24e@linux.vnet.ibm.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16070106-0048-0000-0000-0000019B662C X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16070106-0049-0000-0000-0000460ED424 Message-Id: <20160701060519.GA8863@gwshan> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-07-01_01:,, 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-1607010058 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 01, 2016 at 01:27:17PM +0800, Yongji Xie wrote: >>On Thu, Jun 30, 2016 at 06:53:08PM +0800, Yongji Xie wrote: >>>VF BARs are read-only zeroes according to SRIOV spec, >>>the normal way(writing BARs) of allocating resources wouldn't >>>be applied to VFs. The VFs' resources would be allocated >>>when we enable SR-IOV capability. So we should not try to >>>reassign alignment after we enable VFs. It's meaningless >>>and will release the allocated resources which leads to a bug. >>> >>>Signed-off-by: Yongji Xie >>>--- >>>drivers/pci/pci.c | 4 ++++ >>>1 file changed, 4 insertions(+) >>> >>>diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c >>>index be8f72c..6ae02de 100644 >>>--- a/drivers/pci/pci.c >>>+++ b/drivers/pci/pci.c >>>@@ -4822,6 +4822,10 @@ void pci_reassigndev_resource_alignment(struct pci_dev *dev) >>> resource_size_t align, size; >>> u16 command; >>> >>>+ /* We should never try to reassign VF's alignment */ >>>+ if (dev->is_virtfn) >>>+ return; >>>+ >>Yongji, I think it's correct to ignore VF's BARs. Another concern is: >>it's safe to apply alignment to PF's IOV BARs? Lets have an extreme >>example here: one PF has 16 VFs; each VF has only one 1KB. It means >>the only PF IOV BAR is 16KB. I don't see how it works after expanding >>it to 64KB which is the page size. It might be not a problem on PowerNV >>platform, but potentially a issue on x86? > >Seems like the alignment would not be applied to IOV BARs because >pci_reassigndev_resource_alignment() will be called before >sriov_init(). > Correct, thanks for the claim. I guess the alignment applied to PF IOV BARs should be ignored as well? Anyway, the IOV BARs are retireved from SRIOV capability. It deserves a comment if you plan to take the change. Actually, the comment here (for ignoring alignment to VF BARs) can be improved a bit as well, it'd better why the alignment cannot be applied. Thanks, Gavin