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SubjectRe: reboot via bios on X86_64?
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.

> 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?

--
Matthew Garrett | mjg59@srcf.ucam.org


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