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

[Jason Andryuk]

On 2026-08-06 09:31, Juergen Gross wrote:
> On 06.08.26 15:24, Jason Andryuk wrote:
> > On 2026-08-06 08:00, Jürgen Groß wrote:
> > > 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.
> >
> > I see more reduction:
> > 15029248 - arch/x86/boot/bzImage
> > 15021056 - arch/x86/boot/bzImage.after
> >
> > ~8k
> >
> > 52542480 - vmlinux
> > 52523184 - vmlinux.after
> >
> > ~18k
> >
> > $ ../linux/scripts/bloat-o-meter vmlinux vmlinux.after
> > add/remove: 1/136 grow/shrink: 14/48 up/down: 15902/-22430 (-6528)
>
> Did you disable CONFIG_XEN_PVHVM_GUEST in the before kernel, too?

Yes

$ grep PVHVM config-before config-after config-pvh-before:CONFIG_XEN_PVHVM=y
config-pvh-before:CONFIG_XEN_PVHVM_SMP=y
config-pvh-before:# CONFIG_XEN_PVHVM_GUEST is not set
config-pvh-after:# CONFIG_XEN_PVHVM_GUEST is not set

These three options change:
$ diff -u config-before config-after
-CONFIG_XEN_PVHVM=y
-CONFIG_XEN_PVHVM_SMP=y
-CONFIG_XEN_AUTO_XLATE=y

Regards,
Jason