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Mon, 27 Jul 2020 16:37:45 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 20EB7B2067; Mon, 27 Jul 2020 16:37:45 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id BDAFDB2064; Mon, 27 Jul 2020 16:37:42 +0000 (GMT) Received: from oc4221205838.ibm.com (unknown [9.163.15.127]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Mon, 27 Jul 2020 16:37:42 +0000 (GMT) Subject: Re: [RFC PATCH] s390x/pci: vfio-pci breakage with disabled mem enforcement To: Pierre Morel , Alex Williamson References: <1595517236-17823-1-git-send-email-mjrosato@linux.ibm.com> <20200723102916.7cf15b43@w520.home> <0481c77e-f71f-886b-9b0a-41529eb139ee@linux.ibm.com> From: Matthew Rosato Message-ID: <2a76a044-10ea-b77a-0c20-64748ea7a86c@linux.ibm.com> Date: Mon, 27 Jul 2020 12:37:41 -0400 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: <0481c77e-f71f-886b-9b0a-41529eb139ee@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit 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_11:2020-07-27, 2020-07-27 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 phishscore=0 spamscore=0 suspectscore=0 priorityscore=1501 malwarescore=0 impostorscore=0 bulkscore=0 adultscore=0 lowpriorityscore=0 mlxscore=0 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2007270111 Received-SPF: pass client-ip=148.163.158.5; envelope-from=mjrosato@linux.ibm.com; helo=mx0b-001b2d01.pphosted.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/27 12:37:48 X-ACL-Warn: Detected OS = Linux 3.1-3.10 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 7/27/20 11:40 AM, Pierre Morel wrote: > > > 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. > Thanks for the explanation. > Shouldn't we fix this inside the kernel, to keep older QMEU working? Yes, ideally. > > 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? > From my perspective at least, this would resolve the issue and is in-line with the sort of suggestion Alex floated the other day of "do we need code to deduce that we have a VF based on the existence of MMIO BARs, but lack of memory enable bit?" -- it just sounds like a different way of coming to the conclusion. Effectively we need a way to say: 'for the purposes of memory_enable detection, treat this thing like a virtual function because it is one, even though it doesn't always act like one' > >> >>> @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 >