On 12/17/19 1:32 PM, Alex Williamson wrote:
On Tue, 17 Dec 2019 11:25:38 -0500
Laine Stump <laine@xxxxxxxxx> 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'")
This is the new approach of the series I implemented today and plan to
to send for review today/tomorrow. I realized, after all the discussions
yesterday with Alex, that the patch series would be best just sticking with
what we want fixed (managed=yes and parcial assignment) and leaving
unmanaged (managed=no) configurations alone. If the user has an existing,
working unmanaged setup, this means that the user chose to manage device
detach/re-attach manually and shouldn't be bothered with a change that's
aimed to managed devices.
Thanks,
DHB
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
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