linux-kernel - Re: [QUERY] lguest64

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Message-ID: <51F9005F.30501@zytor.com>
Date:	Wed, 31 Jul 2013 05:17:35 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mike Rapoport <mike.rapoport@...il.com>
CC:	Rusty Russell <rusty@...tcorp.com.au>,
	Ramkumar Ramachandra <artagnon@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [QUERY] lguest64

On 07/31/2013 02:39 AM, Mike Rapoport wrote:
> 
> The use case I had in mind is to use lguest as a nested hypervisor in
> public clouds. As of today, major public clouds do not support nested
> virtualization and it's not clear at all if they will expose this
> ability in their deployments. Addition of 64-bit support for lguest
> won't require changes to pvops and, as far as I can tell, won't change
> the number of pvops users...
> 

"We can add a pvops user and that won't change the number of pvops
users" What?!

>> Yes, the subset of x86-64 machines for which there isn't hardware
>> virtualization support is pretty uninteresting.
> 
> There are plenty virtual machines in EC2, Rackspace, HP and other
> clouds that do not have hardware virtualization. I believe that
> running a hypervisor on them may be pretty interesting.

The big problem with pvops is that they are a permanent tax on future
development -- a classic case of "the hooks problem."  As such it is
important that there be a real, significant, use case with enough users
to make the pain worthwhile.  With Xen looking at sunsetting PV support
with a long horizon, it might currently be possible to remove pvops some
time in the early 2020s or so timeframe.  Introducing and promoting a
new user now would definitely make that impossible.

So it matters that the use case be real.

	-hpa

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