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Mon, 27 Jul 2020 15:40:40 GMT Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 3E74FAE053; Mon, 27 Jul 2020 15:40:40 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A9991AE057; Mon, 27 Jul 2020 15:40:39 +0000 (GMT) Received: from oc3016276355.ibm.com (unknown [9.145.17.84]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 27 Jul 2020 15:40:39 +0000 (GMT) Subject: Re: [RFC PATCH] s390x/pci: vfio-pci breakage with disabled mem enforcement To: Alex Williamson , Matthew Rosato References: <1595517236-17823-1-git-send-email-mjrosato@linux.ibm.com> <20200723102916.7cf15b43@w520.home> From: Pierre Morel Message-ID: <0481c77e-f71f-886b-9b0a-41529eb139ee@linux.ibm.com> Date: Mon, 27 Jul 2020 17:40:39 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <20200723102916.7cf15b43@w520.home> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235, 18.0.687 definitions=2020-07-27_10:2020-07-27, 2020-07-27 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 lowpriorityscore=0 phishscore=0 bulkscore=0 malwarescore=0 mlxlogscore=999 clxscore=1011 mlxscore=0 priorityscore=1501 suspectscore=0 spamscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2007270105 Received-SPF: pass client-ip=148.163.156.1; envelope-from=pmorel@linux.ibm.com; helo=mx0a-001b2d01.pphosted.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/27 11:40:46 X-ACL-Warn: Detected OS = Linux 3.x [generic] [fuzzy] X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: schnelle@linux.ibm.com, david@redhat.com, cohuck@redhat.com, qemu-devel@nongnu.org, pasic@linux.ibm.com, borntraeger@de.ibm.com, qemu-s390x@nongnu.org, rth@twiddle.net Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2020-07-23 18:29, Alex Williamson wrote: > On Thu, 23 Jul 2020 11:13:55 -0400 > Matthew Rosato wrote: > >> I noticed that after kernel commit abafbc55 'vfio-pci: Invalidate mmaps >> and block MMIO access on disabled memory' vfio-pci via qemu on s390x >> fails spectacularly, with errors in qemu like: >> >> qemu-system-s390x: vfio_region_read(0001:00:00.0:region0+0x0, 4) failed: Input/output error >> >> From read to bar 0 originating out of hw/s390x/s390-pci-inst.c:zpci_read_bar(). >> >> So, I'm trying to figure out how to get vfio-pci happy again on s390x. From >> a bit of tracing, we seem to be triggering the new trap in >> __vfio_pci_memory_enabled(). Sure enough, if I just force this function to >> return 'true' as a test case, things work again. >> The included patch attempts to enforce the setting, which restores everything >> to working order but also triggers vfio_bar_restore() in the process.... So >> this isn't the right answer, more of a proof-of-concept. >> >> @Alex: Any guidance on what needs to happen to make qemu-s390x happy with this >> recent kernel change? > > Bummer! I won't claim to understand s390 PCI, but if we have a VF > exposed to the "host" (ie. the first level where vfio-pci is being > used), but we can't tell that it's a VF, how do we know whether the > memory bit in the command register is unimplemented because it's a VF > or unimplemented because the device doesn't support MMIO? How are the > device ID, vendor ID, and BAR registers virtualized to the host? Could > the memory enable bit also be emulated by that virtualization, much > like vfio-pci does for userspace? If the other registers are > virtualized, but these command register bits are left unimplemented, do > we need code to deduce that we have a VF based on the existence of MMIO > BARs, but lack of memory enable bit? Thanks, > > Alex Alex, Matt, in s390 we have the possibility to assign a virtual function to a logical partition as function 0. In this case it can not be treated as a virtual function but must be treated as a physical function. This is currently working very well. However, these functions do not set PCI_COMMAND_MEMORY as we need. Shouldn't we fix this inside the kernel, to keep older QMEU working? Then would it be OK to add a new bit/boolean inside the pci_dev/vfio_pci_device like, is_detached_vfn, that we could set during enumeration and test inside __vfio_pci_memory_enabled() to return true? In the enumeration we have the possibility to know if the function is a HW/Firmware virtual function on devfn 0 or if it is created by SRIOV. It seems an easy fix without side effects. What do you think? > >> @Nilkas/@Pierre: I wonder if this might be related to host device is_virtfn? >> I note that my host device lspci output looks like: >> >> 0000:00:00.0 Ethernet controller: Mellanox Technologies MT27710 Family [ConnectX-4 Lx Virtual Function] >> >> But the device is not marked as is_virtfn.. Otherwise, Alex's fix >> from htps://lkml.org/lkml/2020/6/25/628 should cover the case. >> I do not think we can fix this problem by forcing the is_virtfn bit. AFAIU, our HW virtual function works a lot like a physical function. >> >> >> Matthew Rosato (1): >> s390x/pci: Enforce PCI_COMMAND_MEMORY for vfio-pci >> >> hw/s390x/s390-pci-inst.c | 10 ++++++++++ >> 1 file changed, 10 insertions(+) >> > > Regards, Pierre -- Pierre Morel IBM Lab Boeblingen