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Re: [Xen-devel] shutdown question - PV vs HVM

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] shutdown question - PV vs HVM
From: Russ Blaine <russell.blaine@xxxxxxx>
Date: Wed, 03 Sep 2008 11:01:30 -0700
Cc: James Harper <james.harper@xxxxxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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Have a question on this old thread:

Keir Fraser wrote:
For a PV guest, a shutdown node is written into xenstore which the guest
picks up. The guest will then usually initiate a clean shutdown.

The same happens for an HVM guest with PV drivers installed. If an HVM guest
has no PV drivers (And so will obviously not be watching xenstore) then xend
notifies the shutdown immediately to Xen. This causes Xen to immediately
transition the guest to shutdown state, and no longer execute the guest,
with no chance for clean shutdown. If there are no PV drivers installed,
clean shutdown needs to be initiated from within the guest.

Why are HVM domains treated differently for shutdown? Guest OSes already know how to do a clean ACPI-initiated shutdown, so why not use that for shutdown in the presence of PV drivers?

The current method requires extra complexity in PV drivers. I imagine that it either fell out of porting PV drivers from PV domains to HVM domains or is just paranoia about losing data during ACPI shutdown.

- R

 -- Keir

On 1/10/07 02:13, "James Harper" <james.harper@xxxxxxxxxxxxxxxx> wrote:

I've had a bit of a look through the code but can't seem to find the
answer to this question... what is the method by which 'xm' tells a
domain to shutdown?

What is different about HVM that means it just powers straight off?

Looking at the Linux source, it appears that something is done with
'platform-feature-multiprocessor-suspend' in the store, but it isn't
clear to me what...



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