linux-kernel - Re: Attempt rebooting via port CF9 if it seems to be available

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Date:	Wed, 12 Nov 2008 21:49:10 +0300
From:	Andrey Borzenkov <arvidjaar@...l.ru>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Len Brown <lenb@...nel.org>, Matthew Garrett <mjg@...hat.com>,
	Ingo Molnar <mingo@...e.hu>, Avi Kivity <avi@...hat.com>,
	linux-acpi@...r.kernel.org, Len Brown <len.brown@...el.com>,
	Eduardo Habkost <ehabkost@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Attempt rebooting via port CF9 if it seems to be available

On Wednesday 12 November 2008, H. Peter Anvin wrote:
> Looking at doing the port CF9 fallback, I stumbled onto something fishy.
> 
> I wonder if anyone here happens to have any idea why we turn off
> caching in machine_real_restart()?  Jumping to the BIOS is *not* a
> reset; we jump to the decompressed BIOS on low memory which is usually
> shadowed, not to the BIOS entry point.  In that way, it's more of an
> INIT than a reset, and disabling caching seems broken.
> 
> Either way, here is a preliminary patch to do the CF9 if safe, and then
> falling back to keyboard reboot.  I'm a bit concerned about how to test
> it, of course; this stuff is sensitive and just about impossible to test
> except on millions of machines at once...
> 
> If you have any machines (especially problematic ones) and find that
> this patch either helps or hurts or do nothing, please do let me know so
> I have any idea of the extent of coverage.
> 

Works here both with default and reboot=p.

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