Re: [PATCH v2 1/3] x86: remove PVHv1 code

From: George Dunlap <george.dunlap@citrix.com>
To: Ian Jackson <ian.jackson@eu.citrix.com>,
	Roger Pau Monne <roger.pau@citrix.com>
Cc: Elena Ufimtseva <elena.ufimtseva@oracle.com>,
	Kevin Tian <kevin.tian@intel.com>,
	Tamas K Lengyel <tamas@tklengyel.com>,
	Wei Liu <wei.liu2@citrix.com>,
	Jun Nakajima <jun.nakajima@intel.com>,
	Razvan Cojocaru <rcojocaru@bitdefender.com>,
	George Dunlap <george.dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Paul Durrant <paul.durrant@citrix.com>,
	Jan Beulich <jbeulich@suse.com>,
	xen-devel@lists.xenproject.org
Subject: Re: [PATCH v2 1/3] x86: remove PVHv1 code
Date: Wed, 1 Mar 2017 14:20:13 +0000	[thread overview]
Message-ID: <2e4b54c7-025c-7ae5-f2cb-a9a03b51f362@citrix.com> (raw)
In-Reply-To: <22710.55336.494328.893677@mariner.uk.xensource.com>

On 01/03/17 14:18, Ian Jackson wrote:
> Roger Pau Monne writes ("Re: [PATCH v2 1/3] x86: remove PVHv1 code"):
>> On Wed, Mar 01, 2017 at 01:53:29PM +0000, Ian Jackson wrote:
>>> Well, PVHv2 is in the process of becoming properly supported, so now
>>> is the time to decide the "official" way.
>>
>> I prefer builder="hvm" device_model_version="none" because I think
>> it's clearer from a user PoV that a HVM guest it being
>> created.
> 
> Err, but a PVH guest is not an HVM guest in the sense that the user
> will expect.  Whenever I explain to anyone the difference between PV
> and HVM, the explanation is that "HVM provides a complete emulated PC"
> and "PV needs a guest operating systemn modified to work under Xen".
> By both these measures, a PVH guest is more like PV than HVM.
> 
> The use of the CPU extensions which originally only enabled support
> for HVM is a detail which most people will not be so interested in.
> The details of API, ABI and so on are not of interest to the writer of
> the xl domain config file.
> 
>> OTOH, using pvh=1 it's more obscure, and it isn't clear
>> which kind of guest you are creating, and which options apply to
>> it. Although all that can be fixed in the man page, I think it's
>> less intuitive.
> 
> The explanation we have been giving to ordinary users is that there
> are going to be three kinds of guest: PV, HVM, and the new PVH.

I was in the middle of writing something very similar to the above two
paragraphs, but instead I'll just say that I agree with Ian. :-)

 -George

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