Re: [PATCH 0/4] Xen: Add Q35 initial support for HVM guests

["Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>]

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On Fri, Mar 13, 2026 at 04:46:56PM +0000, Thierry Escande wrote:
> This patch series introduces Q35 chipset support for Xen HVM guests. This is
> based on the work from Alexey Gerasimenko (See patchset [1] for reference).
> 
> This series does not implement device passthrough as this will need more work
> on the Xen side to support multiple PCI buses. Since Q35 chipset does not
> support device hotplugging and with current Xen mechanism for device
> passthrough, they have to be plugged to a new PCIe root port, i.e. not the PCI
> bus 0.

I always found it weird that Xen does hot-plugging of PCI passthrough
devices... Wouldn't it be easier to change this (connect them from the
very start, via QEMU cmdline) and declare hotplug as unsupported (at
least at this time)? I realize it's more complex change at the toolstack
side, but overall may simplify things and maybe even improve
reliability.

In any case, it's probably not worth blocking initial support on this.

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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