On 04.06.25 08:52, Jan Beulich wrote: > On 03.06.2025 15:31, Mykyta Poturai wrote: >> On 02.06.25 11:11, Jan Beulich wrote: >>> On 28.05.2025 11:12, Mykyta Poturai wrote: >>>> From: Stewart Hildebrand <stewart.hildebr...@amd.com> >>>> >>>> Enable the use of IOMMU + PCI in dom0 without having to specify >>>> "pci-passthrough=yes". Due to possible platform specific dependencies >>>> of the PCI host, we rely on dom0 to initialize it and perform >>>> a PHYSDEVOP_pci_device_add/remove call to add each device to SMMU. >>>> PHYSDEVOP_pci_device_reset is left untouched as it does not have the >>>> pci_passthrough_enabled check. >>> >>> Just to re-raise the question here: Is this actually correct? >> >> I'm afraid I don't quite understand your concerns here. >> >> The purpose of this patch is to relax the pci_passthrough_enabled checks >> and make PCI physdev ops work with passthrough disabled. >> The reset op worked independently of PCI passthrough being on or off and >> will continue to do so after this patch. >> If your concerns are about the correctness of allowing reset to always >> work, you specifically requested this behavior in the patches >> implementing it here[1]. > > Right, yet even there I had already asked for possible differing opinions. > Plus the case I had mentioned was specifically Dom0, which fits here. > > Jan
So I've done some testing to see the actual behavior with different combinations of pci-passthrough and iommu switches. With passthrough=off and iommu=on the reset works fine. But with both of them off, it fails because PHYSDEVOP_pci_device_add is not adding anything and therefore pci_get_pdev can't find the pdev. I am not sure which behavior would be the correct one here for passthrought=off and iommu=off. 1. Leave it as is, reset returns -ENODEV and pciback probe fails 2. Add the same check as in add/remove, reset will return -EOPNOTSUPP and pciback probe will also fail 3. Add the same check as in add/remove but return 0 so pciback can probe the device. Maybe you have some thoughts on this. I can't come up with an actual good reason for using pciback without pci-passthrough enabled, outside of maybe "not breaking some abstract scripts". And EOPNOTSUPP seems more descriptive than ENODEV so I strive towards option 2 if everyone okay with that. -- Mykyta
