On 4/29/26 12:35 PM, Jürgen Groß wrote:
Some minor details from the Xen side of things:
On 29.04.26 15:52, Val Packett wrote:
The experimental virtio-mmio support for Xen was initially developed
on aarch64, so device trees were used to configure the mmio devices,
with arbitrary vGIC interrupts used by the hypervisor. On x86_64
however, the only reasonable way to interrupt the guest is over Xen
event channels, which can only be acquired by children of xenbus,
More exact: interdomain event channels need to be connected to a xenbus
device. But you are needing those, so for your use case the above
statement
is correct.
the virtual bus driven by Xen's configuration database, XenStore.
It is also a more convenient and "Xen-ish" way to provision devices.
Implement a xenbus client for virtio-mmio which negotiates an
event channel and provides it as a platform IRQ to the
virtio-mmio driver.
Signed-off-by: Val Packett <[email protected]>
---
Hi,
I've been working on porting virtio-mmio support from Arm to x86_64,
with the goal of running vhost-user-gpu to power Wayland/GPU integration
for Qubes OS. (I'm aware of various proposals for alternative virtio
transports but virtio-mmio seems to be the only one that *is* upstream
already and just Works..) Setting up virtio-mmio through xenbus,
initially
motivated just by event channels being the only real way to get
interrupts
working on HVM, turned out to generally be quite pleasant and nice :)
I'd like to get some early feedback for this patch, particularly
the general stuff:
* is this whole thing acceptable in general?
* should it be extracted into a different file?
* (from the Xen side) any input on the xenstore keys, what goes where?
You should add some documentation in the Xen source tree regarding the
Xenstore keys (see docs/misc/xenstore-paths.pandoc there).
Ack, thanks!
[…]
+again:
+ err = xenbus_transaction_start(&xbt);
No need to use a Xenstore transaction here. The written node(s) are
regarded to be valid only after calling xenbus_switch_state() to set
the frontend state to XenbusStateInitialised.
Oh, I assumed transactions were required for writing from the kernel to
work at all…
[..]
+static const struct xenbus_device_id virtio_mmio_xen_ids[] = {
+ { "virtio" },
Please use "virtio-mmio" here, as I could imagine "virtio-pci"
devices, too.
Ack. Would actually also distinguish it from the initial Arm
proof-of-concept version…
Thanks,
~val
