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

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Message-ID: <m1myggdbzg.fsf@frodo.ebiederm.org>
Date:	Mon, 03 Nov 2008 08:13:07 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Avi Kivity <avi@...hat.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

Avi Kivity <avi@...hat.com> writes:

> Eduardo Habkost wrote:
>> We probably need to disable vmx on all CPUs, but emergency reboot skips
>> native_smp_send_stop() (where we could hook a virt_disable call in).
>>
>> As relying on IPIs defeats the whole point of emergency_restart, a proper
>> fix will need to use NMIs like the kdump code does.
>>
>
> They should use the same code; they have a similar environment at entry and
> reliability requirements for e_r are not greater than kdump's.

Just a sec.

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.

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 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.

Eric

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