Re: [libvirt] [PATCH v4 0/5] PCI hostdev partial assignment support

On Tue, 17 Dec 2019 11:25:38 -0500 Laine Stump <laine(a)laine.org&gt; wrote: > On 12/16/19 6:03 PM, Daniel Henrique Barboza wrote: >> About breaking existing configurations, there is the possibility of not >> going forward with patch 03, which is enforcing this rule of declaring >> all the >> IOMMU group. Existing domains will keep working as usual, the option to >> unassign devices will still be present, but the user will have to deal >> with >> the potential QEMU errors if not all PCI devices were detached from >> the host. >> >> In this case, the 'unassigned' type will become more of a ON/OFF >> switch to >> add/remove the PCI hostdev from the guest without removing it from the >> domain XML. It is still useful, but we lose the idea of all the IOMMU >> devices being described in the domain XML, which is something Laine >> mentioned it would be desirable in one of the RFCs. > > > I don't actually recall saying that :-). I haven't looked in the list > archives, but what I *can* imagine myself saying is that only devices > mentioned in the XML should be manipulated in any way by libvirt. So, +1 > for example, you shouldn't unbind device X from its host driver if there > is nothing in the XML telling you to do that. But if a device isn't > mentioned in the XML, and is already bound to some driver that is > acceptable to the VFIO subsystem (e.g. vfio-pci, pci-stub or no driver > at all (? is that right Alex?)) then that should not create any problem. Yes, that's right. > Doing otherwise would break too many existing configs. (For example, my > own assigned-GPU config, which assumes that all the devices are already > bound to the proper driver, and uses "managed='no'")

Effectively anyone assigning PFs with a PCIe root port that does not support ACS would be broken by this series. That's a significant portion of vfio users. Thanks, Alex