Re: reboot via bios on X86_64?

[Miles Fidelman]

Thanks for the quick response.

Matthew Garrett wrote:
> On Mon, Apr 09, 2012 at 11:39:32AM -0400, Miles Fidelman wrote:
>
> > 1. What's the logic behind this?  Why not enable a bios reboot for 64bit
> > kernels?  Is there any reason why the machine_real_restart code wouldn't
> > work just as well in 64bit mode?  Anybody know the history?
> The bios reboot code requires you to reprogram the CPU to real mode. I
> don't think there's any fundamental reason you can't do that from 64-bit
> mode, but nobody's ever written that code.

That would explain it.  I guess there's a little bit of trickiness 
involved in setting things up before
switching to real mode.

> > 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: someone suggested trying a kexec-reboot, but that's also
> > not supported on my configuration (running over a Xen hypervisor).]
> Windows never uses the equivalent of the BIOS reboot method, so the
> assumption is that if you ever need on Linux to it's because there's a
> bug somewhere else. Does the platform reboot if you run the kernel on
> bare metal rather than under Xen?

No.  Tried all the combinations - w/ and w/o hypervisor, all the 
available kernel options.  Seems
like the only thing that will reboot this particular hardware/bios combo 
is via the bios.

Miles

--
In theory, there is no difference between theory and practice.
In practice, there is.   .... Yogi Berra


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