Re: reboot via bios on X86_64?

From: Miles Fidelman
Date: Mon Apr 09 2012 - 14:07:23 EST

H. Peter Anvin wrote:
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.
ahhh.... ain't things fun when one gets really close to the hardware

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

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