Re: reboot via bios on X86_64?

From: H. Peter Anvin
Date: Mon Apr 09 2012 - 13:53:43 EST

On 04/09/2012 10:26 AM, Miles Fidelman wrote:
> 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.

Actually this code already exists; the difference is that we have to
return to 32-bit mode first.

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