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vfio-pci/zdev: Perform platform specific function reset for zPCI From: Niklas Schnelle To: Farhan Ali , Alex Williamson , Bjorn Helgaas Cc: linux-s390@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, mjrosato@linux.ibm.com Date: Thu, 14 Aug 2025 21:55:00 +0200 In-Reply-To: <350a9bd5-c2a9-4206-98fd-8a7913d36112@linux.ibm.com> References: <20250813170821.1115-1-alifm@linux.ibm.com> <20250813170821.1115-6-alifm@linux.ibm.com> <20250813143034.36f8c3a4.alex.williamson@redhat.com> <7059025f-f337-493d-a50c-ccce8fb4beee@linux.ibm.com> <20250813165631.7c22ef0f.alex.williamson@redhat.com> <5c76f6cfb535828f6586a67bd3409981663d14d8.camel@linux.ibm.com> <350a9bd5-c2a9-4206-98fd-8a7913d36112@linux.ibm.com> Autocrypt: addr=schnelle@linux.ibm.com; prefer-encrypt=mutual; keydata=mQINBGHm3M8BEAC+MIQkfoPIAKdjjk84OSQ8erd2OICj98+GdhMQpIjHXn/RJdCZLa58k /ay5x0xIHkWzx1JJOm4Lki7WEzRbYDexQEJP0xUia0U+4Yg7PJL4Dg/W4Ho28dRBROoJjgJSLSHwc 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TDvz1eGuQVqtb08E0cQjNdbfN+AswK49i7h6UZxyD4lwM3trq3m7QPWLMV1OynXbolQpSDGEt+c /F8mrGnqFkjHUngsETsvgWDyx1zqd+vWYMJs9QUWCb7rkson8dI3MXITok6EqibOZyvKZ7GyHSJ tQlAgUR5coJGlvYbc6aK4Ha+5pCIxDP0NaB64WwsAplZ9LhdRO/BV3YI7OfYCMi0BUMkVwxqDmY I3TYGhwdHeIVl9vEJzOmNJinEnVRVAGFjEz9+uIxduFc8Efy+eFsg5LUaoeewl9Qqg7G3X4KfsF +ZdQJW3B X-Proofpoint-ORIG-GUID: 6UOYz480YT_XhDGQjbyjkdWSLf_EAveW X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-08-13_02,2025-08-14_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 phishscore=0 clxscore=1015 priorityscore=1501 spamscore=0 bulkscore=0 malwarescore=0 adultscore=0 impostorscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2507300000 definitions=main-2508130167 On Thu, 2025-08-14 at 09:33 -0700, Farhan Ali wrote: > On 8/14/2025 6:12 AM, Niklas Schnelle wrote: > > On Wed, 2025-08-13 at 16:56 -0600, Alex Williamson wrote: > > > On Wed, 13 Aug 2025 14:52:24 -0700 > > > Farhan Ali wrote: > > >=20 > > > > On 8/13/2025 1:30 PM, Alex Williamson wrote: > > > > > On Wed, 13 Aug 2025 10:08:19 -0700 > > > > > Farhan Ali wrote: > > > > > =20 > > > > > > For zPCI devices we should drive a platform specific function r= eset > > > > > > as part of VFIO_DEVICE_RESET. This reset is needed recover a zP= CI device > > > > > > in error state. > > > > > >=20 > > > > > > Signed-off-by: Farhan Ali > > > > > > --- > > > > > > arch/s390/pci/pci.c | 1 + > > > > > > drivers/vfio/pci/vfio_pci_core.c | 4 ++++ > > > > > > drivers/vfio/pci/vfio_pci_priv.h | 5 ++++ > > > > > > drivers/vfio/pci/vfio_pci_zdev.c | 39 ++++++++++++++++++++++= ++++++++++ > > > > > > 4 files changed, 49 insertions(+) >=20 --- snip --- > > Now for pci_reset_hotplug_slot() via VFIO_DEVICE_PCI_HOT_RESET I'm not > > sure why that won't work as is. @Farhan do you know? >=20 > VFIO_DEVICE_PCI_HOT_RESET would have been sufficient interface for=20 > majority of PCI devices on s390x as that would drive a bus reset. It was= =20 > sufficient as most devices were single bus devices. But in the latest=20 > generation of machines (z17) we expose true SR-IOV and an OS can have=20 > access to both PF and VFs and so these are on the same bus and can have= =20 > different ownership based on what is bound to vfio-pci. >=20 Talked to Farhan a bit off list. I think the problem boils down to this. The s390 PCI support, due to there always being a hypervisor, does hot and cold plug on a per PCI function basis. And so the hotplug driver's reset_slot() is just a wrapper around zpci_hot_reset_device() and also does per PCI function reset.=C2=A0 Now when doing a VFIO_PCI_HOT_RESET this still doesn't give us a usable per function reset because vfio_pci_ioctl_get_pci_hot_reset_info()'s grouping assumes, quite naturally, that as a slot reset this will reset an entire slot and so the ownership checks fail when we use this reset on e.g. an SR-IOV capable device with PFs + VFs where s390 exposes their PCI topology even while retaining per function hotplug.=C2=A0 As some more background, we've had the virtual PCI topology for SR-IOV capable devices since commit 44510d6fa0c0 ("s390/pci: Handling multifunctions") added in v6.9 but only with z17 will they be generally available. Thanks, Niklas