Messages in this thread | | | Date | Mon, 7 Feb 2022 10:43:34 -0500 | Subject | Re: [PATCH v3 14/30] vfio/pci: re-introduce CONFIG_VFIO_PCI_ZDEV | From | Matthew Rosato <> |
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On 2/7/22 3:35 AM, Cornelia Huck wrote: > On Fri, Feb 04 2022, Matthew Rosato <mjrosato@linux.ibm.com> wrote: > >> This was previously removed as unnecessary; while that was true, subsequent >> changes will make KVM an additional required component for vfio-pci-zdev. >> Let's re-introduce CONFIG_VFIO_PCI_ZDEV as now there is actually a reason >> to say 'n' for it (when not planning to CONFIG_KVM). > > Hm... can the file be split into parts that depend on KVM and parts that > don't? Does anybody ever use vfio-pci on a non-kvm s390 system? >
It is possible to split out most of the prior CLP/ vfio capability work (but it would not be a totally clean split, zpci_group_cap for example would need to have an inline ifdef since it references a KVM structure) -- I suspect we'll see more of that in the future. I'm not totally sure if there's value in the information being provided today -- this CLP information was all added specifically with userspace->guest delivery in mind. And to answer your other question, I'm not directly aware of non-kvm vfio-pci usage on s390 today; but that doesn't mean there isn't any or won't be in the future of course. With this series, you could CONFIG_KVM=n + CONFIG_VFIO_PCI=y|m and you'll get the standard vfio-pci support but never any vfio-pci-zdev extension.
If we wanted to provide everything we can where KVM isn't strictly required, then let's look at what a split would look like:
With or without KVM: zcpi_base_cap zpci_group_cap (with an inline ifdef for KVM [1]) zpci_util_cap zpci_pfip_cap vfio_pci_info_zdev_add_caps vfio_pci_zdev_open (ifdef, just return when !KVM [1]) vfio_pci_zdev_release (ifdef, just return when !KVM [1])
KVM only: vfio_pci_zdev_feat_interp vfio_pci_zdev_feat_aif vfio_pci_zdev_feat_ioat vfio_pci_zdev_group_notifier
I suppose such a split has the benefit of flexibility / future-proofing... should a non-kvm use case arrive in the future for s390 and we find we need some s390-specific handling, we're still building vfio-pci-zdev into vfio-pci by default and can just extend that.
[1] In this case I would propose renaming CONFIG_VFIO_PCI_ZDEV as we would once again always be building some part of vfio-pci-zdev with vfio-pci on s390 -- maybe something like CONFIG_VFIO_PCI_ZDEV_KVM (wow that's a mouthful) and then use this setting to check "KVM" in my above split. Since this setting will imply PCI, VFIO_PCI and KVM, we can then s/CONFIG_VFIO_PCI_ZDEV/CONFIG_VFIO_PCI_ZDEV_KVM/ for the rest of the series (to continue covering cases like we build KVM but not pci, or not vfio-pci)
How does that sound?
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