Preliminary kexec support for Linux/m68k

Geert Uytterhoeven
2013-09-17T10:02:13Z

This is a preliminary set of patches to add kexec support for m68k.

- Kexec only, no kdump support yet (do you have enough RAM to keep a
crashdump kernel in memory at all times? ;-)

- Tested on ARAnyM only. No support for other CPU/MMUs than 68040.

- Although the code contains some phys/virt conversions, it will probably
fail miserably on platforms where kernel virtual addresses are different
from physical address.

- To have automatic "kexec -e" on reboot, copy /etc/rc6.d/S85kexec from
another system, and fix it up for kexec living in /usr/local/sbin instead
of /sbin.

- Sample invocation:

kexec -d -l vmlinux --reuse-cmdline

KERNEL:

Patches:
- [PATCH 1/3] m68k: Add preliminary kexec support
- [PATCH 2/3] m68k: Add support to export bootinfo in procfs
- [PATCH 3/3] [RFC] m68k: Add System RAM to /proc/iomem

Notes:
- The bootinfo is now saved and exported to /proc/bootinfo, so kexec-tools
can read it and pass it (possibly after modification) to the new kernel.
This is similar to /proc/atags on ARM.

- We should create arch/m68k/include/uapi/asm/bootinfo.h (and probably a few
more, e.g. machine-specific model IDs), as this is needed by both m68kboot
and kexec-tools.

- I based [PATCH 3/3] on the PowerPC version, but it's no longer needed as we
now get this information from the bootinfo.
Does anyone think this is nice to have anyway?

KEXEC-TOOLS:

Patches:
- [PATCH 1/2] kexec: Let slurp_file_len() return the number of bytes
- [PATCH 2/2] kexec: Add preliminary m68k support

Notes:
- Based on git://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git

- Tagged bootinfo is read from /proc/bootinfo by default, but this can be
overridden using --bootinfo. No bootinfo editor is provided.
The kexec command will replace/delete command line and ramdisk tags in the
bootinfo.

- The ramdisk is loaded at the top of memory minus 4096, unlike with
m68boot (ataboot/amiboot), as locate_hole() seems to have a bug that it
cannot reserve a block at the real top of memory.

- The first unused page of the kernel image (at address zero) is
automatically removed, just like m68kboot does.
If I don't do this, relocate_new_kernel() fails with a "cannot handle
kernel paging request at address NULL" exception, although the MMU is
disabled at that point.
As m68kboot does this too, I guess this is OK?

- Do we want to check the struct bootversion at the start of the kernel,
like m68kboot does?
Kexec may be used to load ELF files that are not Linux kernel images,
and thus don't have a Linux-specific struct bootversion.

- Do we want to check the size of the kernel image + bootinfo, and warn the
user if it's larger than 4 MiB?
This is a limitation of the current Linux/m68k kernel only.

All comments are welcome!
Have fun! ;-)

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds