linux-kernel - Re: [PATCH 15/15] Revert "x86: default to reboot via ACPI"

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Date:	Thu, 6 Nov 2008 15:30:21 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Eduardo Habkost <ehabkost@...hat.com>
Cc:	Avi Kivity <avi@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Simon Horman <horms@...ge.net.au>,
	Andrew Morton <akpm@...l.org>, Vivek Goyal <vgoyal@...hat.com>,
	Haren Myneni <hbabu@...ibm.com>,
	Andrey Borzenkov <arvidjaar@...l.ru>, mingo@...hat.com,
	"Rafael J. Wysocki" <rjw@...k.pl>, kexec@...ts.infradead.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 15/15] Revert "x86: default to reboot via ACPI"


* Eduardo Habkost <ehabkost@...hat.com> wrote:

> On Thu, Nov 06, 2008 at 08:14:45AM +0100, Ingo Molnar wrote:
> > 
> > * Eduardo Habkost <ehabkost@...hat.com> wrote:
> > 
> > > This reverts commit c7ffa6c26277b403920e2255d10df849bd613380.
> > > 
> > > Now that we have the hooks to disable virtualization on
> > > emergency_restart(), we can get back to the BOOT_KBD reboot_type default.
> > > 
> > > Signed-off-by: Eduardo Habkost <ehabkost@...hat.com>
> > 
> > hm, why revert this? There's nothing wrong with the ACPI reboot 
> > method, it's just that we surprise the BIOS by exiting with an unclean 
> > VMX state in certain circumstances.
> > 
> > if the ACPI reboot method does not work we do the KBD method as the 
> > next thing in the reboot chain.
> 
> I suppose there are cases where the new default broke without KVM, 
> and the suggestion was to disable VMX before rebooting instead of 
> changing the default.
> 
> Avi changed the default because on some machines reboot=kbd breaks 
> when VMX is enabled, but the regressions caused by the new default 
> doesn't necessarily involve VMX.

there's another reason as well: a growing quirk-list of machines where 
ACPI is the best (sometimes only) method to reboot.

> Andrey Borzenkov's patch, for example, adds a new DMI entry because 
> reboot=acpi breaks his keyboard (even without KVM, I guess). Andrey, 
> was that the case?

hm, IIRC the problem was KVM in his case too.

	Ingo
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