On Tue, 2025-10-28 at 09:11 +0800, Bibo Mao wrote:
On 2025/10/27 下午8:29, Niklas Schnelle wrote:
On Wed, 2025-10-22 at 14:24 -0700, Farhan Ali wrote:
On s390 systems, which use a machine level hypervisor, PCI devices are always accessed through a form of PCI pass-through which fundamentally operates on a per PCI function granularity. This is also reflected in the s390 PCI hotplug driver which creates hotplug slots for individual PCI functions. Its reset_slot() function, which is a wrapper for zpci_hot_reset_device(), thus also resets individual functions.
Currently, the kernel's PCI_SLOT() macro assigns the same pci_slot object to multifunction devices. This approach worked fine on s390 systems that only exposed virtual functions as individual PCI domains to the operating system. Since commit 44510d6fa0c0 ("s390/pci: Handling multifunctions") s390 supports exposing the topology of multifunction PCI devices by grouping them in a shared PCI domain. When attempting to reset a function through the hotplug driver, the shared slot assignment causes the wrong function to be reset instead of the intended one. It also leaks memory as we do create a pci_slot object for the function, but don't correctly free it in pci_slot_release().
Add a flag for struct pci_slot to allow per function PCI slots for functions managed through a hypervisor, which exposes individual PCI functions while retaining the topology.
I wonder if LoongArch which now also does per PCI function pass-through might need this too. Adding their KVM maintainers.
Hi Niklas,
Thanks for your reminder. Yes, LoongArch do per PCI function pass-throught. In theory, function pci_slot_enabled_per_func() should return true on LoongArch also. Only that now IOMMU driver is not merged, there is no way to test it, however we will write down this as a note inside about this issue and verify it once IOMMU driver is merged.
Regards Bibo Mao
Hi Bibo,
Is your ability to test if it works for you also hindered for my other patch touching pci_scan_slot()? It sounded like Huacai was looking into testing that.
Thanks, Niklas