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

[Jason Andryuk <jason.andryuk@amd.com>]

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