Re: [libvirt] [PATCH 00/26] Support multiple PHBs for pSeries guests

Now for a slightly more serious overview; more details can be obtained by reading the bug report[1]. There are two main goals behind this series:   1) allow the use of multiple PHBs for pSeries guests;   2) isolate hostdevs from emulated devices. By implementing these changes, pSeries guests running on QEMU/KVM become more similar to those running on PowerVM, which is great for admins. It also makes it possible to have better error detection / recovery. The first part involves convincing libvirt that a guest can have more than a single pci-root controller, which is something that was explicitly forbidden until now. Only pSeries guests get to follow the new rules, of course. Once PHBs are usable, it makes sense to just use them for pretty much everything on pSeries guests. pci-bridge is no longer needed, which is good because it probably never really worked on such guests. To match PowerVM's behavior and provide better isolation, hostdevs should be assigned each their own PHB. Well, almost: the exact requirement is one PHB per host IOMMU group, with the default PHB being reserved for emulated devices. To achieve this, the concept of "isolation group"[2] is introduced: each PHB is assigned one, and only devices that match it will be automatically assigned to that PHB. For hostdevs, the isolation group is the same as the host IOMMU group; emulated devices are assigned the default isolation group, same as the default PHB. It all works out. The implementation is basically complete, minus the documentation. I'm debating whether the current handling of the default isolation group is good or not, but the ideas are all there and I expect I'll need a couple of respins to get all the details right, so feel free to start reviewing :) [1] https://bugzilla.redhat.com/show_bug.cgi?id=1280542 [2] Named like that because, at least for me, "IOMMU" is     basically a tongue twister --  Andrea Bolognani / Red Hat / Virtualization