reboot.c and X86-64 architectures

[Jim Cromie]

On Tue, Apr 3, 2012 at 9:22 PM, Miles Fidelman
<mfidelman at meetinghouse.net> wrote:
>
> Hello Folks,
>
> Perhaps someone here can help me understand the behavior of the kernel reboot code.
>
> I've recently migrated from running a 32bit kernel to a 64bit one
> (specifically Debian Lenny 32bit environment to 2.6.32-5-xen-amd64 on
> top of xen-4.0-amd64 hypervisor build).
>
> This is a somewhat older, and apparently quirky, hardware box.  I've
> found that the only way to reboot it, short of power cycling, is jumping
> through the bios - using the "reboot=bios" kernel option at boot time
> works just fine for an X86_32 kernel.  But... this doesn't work with the
> 64bit kernel.
>
> Pouring through both the documentation and the code for
> arch/x86/kernel/reboot.c yields the very specific admonition (in comments
> describing command-line kernel options), that reboot=bios (Reboot by jumping
> through the BIOS) only applies to X86_32 - and the case statements in the
> code seem to align with the comment.
>
> None of the other available command line options seem to work with my
> hardware, which leads to two questions:
>
> 1. What's the logic behind this?  Why not enable a bios reboot for 64bit
> kernels?  Anybody know the history?
>
> 2. Anybody know a workaround, short of patching and compiling a custom
> kernel? Are there other paths through the reboot code that can invoke a bios
> reboot?  (Note: None of the available command line options seem to work on
> this particular box/bios combination, and kexec-reboot is not available
> for this combination of kernel and hypervisor).
>

perhaps you should try a non-hypervisor kernel.
I have no experience with one, but it could be the issue.
Virtualization developers tend to have big fast modern boxes,
and as you say, yours isnt so modern.

It might be worth a bug report if it appears to be hypervisor related,
but you are on an old kernel too.  Is Lenny current, or is it Sarge ?
maybe a debian upgrade is easier than a current (3.3) kernel build,
but latter is pretty easy.


> Thank you very much,
>
> Miles Fidelman
>
> --
> In theory, there is no difference between theory and practice.
> In practice, there is.   .... Yogi Berra
>
>
>
>
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