Re: Problem with PCI-passthrough to PV guest

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On Wed, May 06, 2026 at 11:18:28AM +0200, Roger Pau Monné wrote:
> On Wed, May 06, 2026 at 10:45:49AM +0200, Jürgen Groß wrote:
> > On 05.05.26 20:47, Roger Pau Monné wrote:
> > > On Tue, May 05, 2026 at 05:53:31PM +0200, Jürgen Groß wrote:
> > > > SUSE QA is seeing a problem with PCI-passthrough of a SR-IOV to a PV 
> > > > guest
> > > > running a 6.4 based kernel, but I can reproduce the problem with 
> > > > upstream
> > > > kernel, too.
> > 
> > Uh, seems my tested kernel was only "nearly upstream" (it was an early
> > 7.0 kernel). It was missing commit 0949c646d646, which makes the difference.
> > 
> > So for now this issue will only show up for cases where a PV-guest is
> > setup for PCI passthrough and it gets memory hotplugged before the PCI
> > device is added to it.
> 
> Hm, yes, this is yet more fallout from the unpopulated-alloc changes.
> For PV guests that have the e820 host available we could try to create
> the hotplug regions over what are host RAM region in the memory map,
> as then we know we won't be overlapping with MMIO areas.

FWIW, my Linux testing series also(?) found a PV PCI-passthrough issue
in recent Linux (linux-next from a few days ago there). While it looks
to be a different issue, it would help a lot to have that series in, to
at least detect regressions early. See
https://lore.kernel.org/xen-devel/cover.30e6171ddf1c6a72eadf4af0a77c892d4f18d811.1777898148.git-series.marmarek@xxxxxxxxxxxxxxxxxxxxxx/

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

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