On Mon, 16 Dec 2019 20:24:56 -0300 Daniel Henrique Barboza <danielhb413@gmail.com> wrote:
On 12/16/19 8:06 PM, Alex Williamson wrote:
On Mon, 16 Dec 2019 17:28:28 -0500 Cole Robinson <crobinso@redhat.com> wrote:
On 12/16/19 8:36 AM, Daniel Henrique Barboza wrote:
changes from version 3 [1]:
Thanks for catching this! PCIe root ports or bridges being part of an IOMMU group is part of the nature of the grouping. However, only endpoint devices can be bound to vfio-pci and thus participate in this "partial assignment". If the code is trying to force all other devices in the IOMMU group that aren't assigned into this partial assignment mode, that's just fundamentally broken. Thanks,
The code isn't forcing a device to be assigned to the guest. It is forcing all the IOMMU devices to be declared in the domain XML to be detached from the host.
Detached from the host by unbinding from host drivers and binding to vfio-pci and "partially" assigned to the guest? That's wrong, we can't do that. Not only will vfio-pci not bind to anything but endpoints, you'll break the host binding bridges that might be part of the group, and there are valid use cases for sequestering a device with pci-stub rather than vfio-pci to add another barrier to the user getting access to the device.
What I did was to extend a verification Libvirt already does, to check for PCI devices of the same IOMMU X being used by other domains, to check the the host as well. Guest start fails if there is any device left in IOMMU X that's not present in the domain.
Yep, can't do that.
In short, the code is implying that all IOMMU devices must be detached from the host, regardless of whether they're going to be used in the guest, regardless of whether they are PCI root ports or bridges. Is this assumption correct, considering kernel/QEMU?
Nope, please don't do this. Thanks, Alex