7:58 p.m.
On Wed, Jan 6, 2016 at 4:43 PM, Laine Stump <laine(a)laine.org> wrote:
On 12/23/2015 11:01 AM, Ziviani . wrote:
Hi Laine,
This (hot plugging all functions at once) is something I was thinking
about. What if we could create a xml file passing the IOMMU group instead
of only one function per time, would it be feasible?
I could start working on a proof of concept if the community thinks it's a
valid path.
Do you know how is currently working on it? I could offer some help if
they need.
(Please reply inline rather than top-posting. It makes it much easier to
follow the context of the conversation.)
What do you mean by "passing the IOMMU group"? Do you mean *just* the
iommu group, excluding the information about the devices? This doesn't seem
like a good idea, since afaik the iommu group number is something just
conjured up by the kernel at boot time, and isn't necessarily predictable
or stable between host reboots. Also, it wouldn't allow for assigning only
some of the devices/functions in a group while leaving others inactive.
My first idea was doing something like this:
% virsh nodedev-dumpxml pci_0000_00_16_3
<device>
<name>pci_0000_00_16_3</name>
[snip]
<iommuGroup number='4'>
<address domain='0x0000' bus='0x00' slot='0x16'
function='0x0'/>
<address domain='0x0000' bus='0x00' slot='0x16'
function='0x3'/>
</iommuGroup>
</capability>
</device>
If an user wants to attach pci_0000_00_16_3, I'd find all devices belonging
the its same iommu group to attach every one. A very poor pseudo-code would
be like:
slot = get_available_guest_slot();
immou_group = device_to_be_attached().get_iommu();
for (device : iommu_group.devices()) {
(1st iteraction) device_add
vfio-pci,host=00:16.0,addr=slot.0,multifunction=on
(2nd iteraction) device_add
vfio-pci,host=00:16.3,addr=slot.3,multifunction=on
}
So, in this case, we could accept either the device to be attached or
simply its current iommu group#.
I think there are two reasonable possibilities:
1) Follow the apparent path of qemu - accept separate attach calls, one
for each function, and use the attach of function 0 as the "action" button
that causes all the functions to be attached.
2) Enhance the attach API to accept multiple <hostdev> elements in the XML
for a single call, and do "whatever is proper for the current hypervisor"
to attach them.
I think my first idea has more to do with you 1st option. But I like the
second one: user specify all devices in the xml, then we assert there is no
missing function, then we go attaching one by one (
with this another poor pseudo-code):
slot = get_available_guest_slot();
for (device : devices_parsed_from_xml()) {
(1st iteraction) device_add
vfio-pci,host=00:16.0,addr=slot.0,multifunction=on
(2nd iteraction) device_add
vfio-pci,host=00:16.3,addr=slot.3,multifunction=on
}
As for detach, it's really only possible to detach *all* functions, and it
would take more bookkeeping to allowing marking each function for removal
and then removing the device when all functions had been marked, so maybe
we only allow detach of function 0, and that will always detach everything?
(not sure, that's just an idea).
I think we can let users detach anyone. We could get the slot and start
detaching all functions from that slot, again another poor example:
device = device_to_be_detached();
for (uint function = 0; function < device.len_slot(), ++function)
detach(device.slot[function]->addr);
As far as I know, nobody is currently working on anything like this for
libvirt, so this is your chance to get your hands dirty!
Awesome! :)
(It just occurred to me that method (1) of multifunction attach method
outlined above will also need similar extra bookkeeping, just as the "mark
each function for removal" detach method would, and this extra bookkeeping
would need to survive a restart of libvirtd in the middle of a series of
attach/detach calls, making it more complicated, so maybe the 2nd methods
would be better. I'd love to hear opinions though.)
Because it's possible to retrieve the functions belonging to a slot I think
we can avoid such bookkeeping (of course, my idea can be totally wrong) :D
(qemu) info pci
...
Bus 0, device 6, function 0:
Class 1920: PCI device 8086:9c3a
IRQ 11.
BAR0: 64 bit memory at 0x40000000 [0x4000001f].
id ""
Bus 0, device 6, function 3:
Serial port: PCI device 8086:9c3d
IRQ 6.
BAR0: I/O at 0x1000 [0x1007].
BAR1: 32 bit memory at 0x40001000 [0x40001fff].
id ""
But based on my code above, the function device_to_be_detached() could
return the struct with slot[functions] based on this qemu info.
Thank you for your time and advice, I'm starting to look on it and let you
know the progress. My irc nickname is #ziviani.
Thank you :)
On Mon, Dec 21, 2015 at 3:53 PM, Laine Stump <laine(a)laine.org> wrote:
> On 12/21/2015 08:29 AM, Ziviani . wrote:
>
> Hello list!
>
> I'm new here and interested in hot-plug multi-function PCI devices.
> Basically I'd like to know why Libvirt does not support it. I've been
> through the archives and basically found this thread:
>
> <https://www.redhat.com/archives/libvir-list/2011-May/msg00457.html>
> https://www.redhat.com/archives/libvir-list/2011-May/msg00457.html
>
> But Qemu seems to handle it accordingly:
> virsh qemu-monitor-command --hmp fedora-23 'device_add
> vfio-pci,host=00:16.0,addr=08.0'
> virsh qemu-monitor-command --hmp fedora-23 'device_add
> vfio-pci,host=00:16.3,addr=08.3'
>
> GUEST:
> # lspci
> (snip)
> 00:08.0 Communication controller: Intel Corporation 8 Series HECI #0 (rev
> 04)
> 00:08.3 Serial controller: Intel Corporation 8 Series HECI KT (rev 04)
>
> However, using Libvirt:
>
> % virsh attach-device fedora-23 pci_0000_00_16_0.xml --live
> Device attached successfully
>
> % virsh attach-device fedora-23 pci_0000_00_16_3.xml --live
> error: Failed to attach device from pci_0000_00_16_3.xml
> error: internal error: Only PCI device addresses with function=0 are
> supported
>
> I made some changes on domain_addr.c[1] for testing and it worked.
>
> [1]https://gist.github.com/jrziviani/1da184c7fd0b413e0426
>
> % virsh attach-device fedora-23 pci_0000_00_16_3.xml --live
> Device attached successfully
>
> GUEST:
> # lspci
> (snip)
> 00:08.0 Communication controller: Intel Corporation 8 Series HECI #0 (rev
> 04)
> 00:08.3 Serial controller: Intel Corporation 8 Series HECI KT (rev 04)
>
> So there is more to it that I'm not aware?
>
>
> You're relying on behavior in the guest OS for which there is no standard
> (and which, by definition, doesn't work on real hardware, so no guest OS
> will be expecting it; a friend more familiar with this has told me that
> probably qemu is sending an (acpi?) "device check" to the guest for each
> function that is added, and in your case it's apparently "doing the right
> thing" in response to that). But just because it is successful in this one
> case doesn't mean that it will be successful in all situations; likely it
> won't be. So while the qemu monitor takes the laissez-faire approach of
> allowing you to try it and letting you pick up the pieces when it fails,
> libvirt prevents it because it is bound to fail, and thus not supportable.
>
> There has recently been some work in qemu to "save up" any requests to
> attach devices with function > 0, then present them all to the guest at
> once when function 0 is attached. This is the only standard way to handle
> hotplug of multiple functions in a slot. Hot unplug can only happen for all
> functions in the slot at once. I'm not sure of the current status of that
> work, but once it is in and stable, libvirt will support it.
>
>
> Thank you!
>
>
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