linux-kernel - Re: [PATCH] Use BIOS reboot on Toshiba Portege 4000

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Date:	Tue, 04 Nov 2008 12:47:23 +0200
From:	Avi Kivity <avi@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Eduardo Habkost <ehabkost@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Andrey Borzenkov <arvidjaar@...l.ru>, mingo@...hat.com,
	Andrew Morton <akpm@...l.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Use BIOS reboot on Toshiba Portege 4000

Eric W. Biederman wrote:
> I think we are confusing two issues here.
>
> - Ordinary machine_restart which happens to call emergency_restart.
>   And is proceeded by machine_shutdown.
>
> - And emergency_restart itself.
>
> To some extent I would be a lot happier if Alt-sysrq-r did what
> was necessary to get into a context where it can call machine_restart
> or even better kernel_restart().
> emergency_restart() is a nice idea but is broken by design.
>
>   

Isn't emergency_restart() equivalent to kexec()?  Both start from 
indeterminite conditions.

> That said.  If we can turn off vmx on that one processor.
> That should be enough for the cpu to triple fault and let
> the BIOS do what it needs to do on that cpu i.e. outb(magic, 0x92)
> and toggle a motherboard level reset?
>
>   

If triple fault is wired to INIT (as it is at least on some systems; for 
example one of mine) then the cpu will reset, but why will the bios 
proceed to issue a motherboard reset?  Won't it happily POST it's way to 
boot (leaving the other cpus dead)?

> If I read the earlier comments correctly the deep issue is
> that going through ACPI to reset systems is less reliable than
> doing it the classic way.
>   

It depends on the system; both are unreliable.  But if we use the same 
trick as with kdump (NMI SIPI + vmxoff) the choice will be orthogonal to 
whether vmx is in use or not.

-- 
error compiling committee.c: too many arguments to function

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