linux-kernel - Lots of XEN init functions called in non-XEN environment

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Date:   Sat, 9 Jul 2022 18:29:14 +0200
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Jürgen Groß <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>
Cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Lots of XEN init functions called in non-XEN environment

Dear Linux folks,


Booting Debian’s Linux kernel with `initcall_debug` on a laptop with no 
XEN being used, I see a lot of Xen related init functions to be called.

```
$ sudo dmesg | grep -e balloon -e xen
[    0.066207] calling  xen_cons_init+0x0/0x50 @ 0
[    0.066210] initcall xen_cons_init+0x0/0x50 returned 0 after 0 usecs
[    0.096491] calling  xen_pvh_gnttab_setup+0x0/0x34 @ 1
[    0.096491] initcall xen_pvh_gnttab_setup+0x0/0x34 returned -19 after 
0 usecs
[    0.100353] calling  xenbus_init+0x0/0x322 @ 1
[    0.100353] initcall xenbus_init+0x0/0x322 returned -19 after 0 usecs
[    0.100353] calling  register_xen_pci_notifier+0x0/0x2d @ 1
[    0.100353] initcall register_xen_pci_notifier+0x0/0x2d returned 0 
after 0 usecs
[    0.100353] calling  xen_pcpu_init+0x0/0xb5 @ 1
[    0.100353] initcall xen_pcpu_init+0x0/0xb5 returned -19 after 0 usecs
[    0.169465] calling  balloon_init+0x0/0x1e0 @ 1
[    0.169467] initcall balloon_init+0x0/0x1e0 returned -19 after 0 usecs
[    0.169470] calling  xen_setup_shutdown_event+0x0/0x30 @ 1
[    0.169473] initcall xen_setup_shutdown_event+0x0/0x30 returned -19 
after 0 usecs
[    0.169476] calling  xenbus_probe_backend_init+0x0/0x6b @ 1
[    0.169482] initcall xenbus_probe_backend_init+0x0/0x6b returned 0 
after 0 usecs
[    0.169485] calling  xenbus_probe_frontend_init+0x0/0x4f @ 1
[    0.169489] initcall xenbus_probe_frontend_init+0x0/0x4f returned 0 
after 0 usecs
[    0.169491] calling  xen_acpi_pad_init+0x0/0x3c @ 1
[    0.169493] initcall xen_acpi_pad_init+0x0/0x3c returned -19 after 0 
usecs
[    0.257640] calling  xenfb_init+0x0/0x3b @ 1
[    0.257642] initcall xenfb_init+0x0/0x3b returned -19 after 0 usecs
[    0.259498] calling  xenbus_probe_initcall+0x0/0x6f @ 1
[    0.259599] initcall xenbus_probe_initcall+0x0/0x6f returned 0 after 
98 usecs
[    0.259615] calling  xenbus_init+0x0/0x3b @ 1
[    0.259617] initcall xenbus_init+0x0/0x3b returned -19 after 0 usecs
[    0.259620] calling  xenbus_backend_init+0x0/0x44 @ 1
[    0.259622] initcall xenbus_backend_init+0x0/0x44 returned -19 after 
0 usecs
[    0.259666] calling  xen_late_init_mcelog+0x0/0x5e @ 1
[    0.259668] initcall xen_late_init_mcelog+0x0/0x5e returned -19 after 
0 usecs
[    0.259811] calling  xen_hvc_init+0x0/0x1de @ 1
[    0.259813] initcall xen_hvc_init+0x0/0x1de returned -19 after 0 usecs
[    0.263794] calling  xenkbd_init+0x0/0x3b @ 1
[    0.263796] initcall xenkbd_init+0x0/0x3b returned -19 after 0 usecs
[    0.285181] calling  balloon_wait_finish+0x0/0xda @ 1
[    0.285183] initcall balloon_wait_finish+0x0/0xda returned -19 after 
0 usecs
```

All these drivers(?) are enabled in Debian’s Linux configuration to also 
support XEN setups, but I wonder, if the system can’t detect once if 
it’s running in a XEN environment, and if it’s not then to skip all the 
XEN related init functions.


Kind regards,

Paul