Re: [PATCH 0/2] xen: Fix PV-only build

[Jürgen Groß]

On 06.08.26 13:31, Jan Beulich wrote:
> On 06.08.2026 12:55, Juergen Gross wrote:
> > On 06.08.26 03:52, Jason Andryuk wrote:
> > > Allow disabling XEN_PVHVM for a PV-only.  A stub in the event channel
> > > code needs to be fixed first.
> > >
> > > Jason Andryuk (2):
> > >     xen/events: Fix xen_set_upcall_vector stub
> > >     xen/Kconfig: select XEN_PVHVM
> > >
> > >    arch/x86/xen/Kconfig             | 8 +++++---
> > >    drivers/xen/events/events_base.c | 2 +-
> > >    2 files changed, 6 insertions(+), 4 deletions(-)
> >
> > I did a comparison of a kernel built with your patches disabling XEN_PVHVM
> > and my patches with XEN_PVHVM_GUEST disabled.
> >
> > The kernel built with my patches is 6 bytes smaller than the one with your
> > patches.
>
> Isn't this a sign of something else needing tweaking, somewhere?

This is a sign that there are probably only very few really HVM specific paths
(in the sense of: explicitly not marked as irrelevant for PV) in the kernel.
Yes, I'm sure you can find some more, but I'm really not sure this is relevant
for more than a handful of users.

> > So I don't see any reason to take your patches, which conflict with mine,
> > especially as my patches have a negative diffstat on source level, too.
>
> Hmm, Jason's patches look to move things into a more adequate direction,
> though. In which case I think a negative diffstat becomes an irrelevant
> argument?

Depends on what you are looking for.

My take from this is that a PV-only kernel with Jason's patches is not really
adding any value, while my simplification is at least making things simpler
in terms of code volume and number of Xen related config options.

Of course it would be possible to have a smaller PV-only kernel, but as I said
already, there has been no public demand for that in the last years and the
downsides IMHO far outweigh the potential gain.

IMO the "adequate direction" regarding Xen specific kernel code is towards PVH
and not towards more PV specific tweaking. And I'm very sure the kernel
community outside of the Xen community is agreeing with me here.


Juergen

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