linux-kernel - Re: [Xen-devel] HVMLite / PVHv2

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Date:	Thu, 14 Apr 2016 11:13:49 +0100
From:	George Dunlap <george.dunlap@...rix.com>
To:	"Luis R. Rodriguez" <mcgrof@...nel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Roger Pau Monné <roger.pau@...rix.com>,
	Matt Fleming <matt@...eblueprint.co.uk>, <jeffm@...e.com>,
	Michael Chang <MChang@...e.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jim Fehlig <jfehlig@...e.com>, Jan Beulich <JBeulich@...e.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Daniel Kiper <daniel.kiper@...cle.com>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Takashi Iwai <tiwai@...e.de>,
	Vojtěch Pavlík <vojtech@...e.cz>,
	Gary Lin <GLin@...e.com>,
	xen-devel <xen-devel@...ts.xenproject.org>,
	Jeffrey Cheung <JCheung@...e.com>,
	Juergen Gross <jgross@...e.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Julien Grall <julien.grall@...aro.org>, joeyli <jlee@...e.com>,
	Borislav Petkov <bp@...en8.de>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Charles Arndol <carnold@...e.com>,
	"Andrew Cooper" <andrew.cooper3@...rix.com>,
	Julien Grall <julien.grall@....com>,
	"Andy Lutomirski" <luto@...capital.net>,
	David Vrabel <david.vrabel@...rix.com>,
	<torvalds@...ux-foundation.org>
Subject: Re: [Xen-devel] HVMLite / PVHv2 - using x86 EFI boot entry

On 13/04/16 20:14, Luis R. Rodriguez wrote:
> On Wed, Apr 13, 2016 at 03:02:26PM -0400, Konrad Rzeszutek Wilk wrote:
>> On Wed, Apr 13, 2016 at 08:50:10PM +0200, Luis R. Rodriguez wrote:
>>> On Wed, Apr 13, 2016 at 11:54:29AM +0200, Roger Pau Monné wrote:
>>>> On Fri, Apr 08, 2016 at 11:58:54PM +0200, Luis R. Rodriguez wrote:
>>>>> OK thanks for the clarification -- still no custom entries for Xen!
>>>>> We should strive for that, at the very least.
>>>>>
>>>>> You do have a point about the legacy stuff. There are two options there:
>>>>>
>>>>>   * Fold legacy support under HVMLite -- which seems to be what we
>>>>>     currently want to do (we should evaluate the implications and
>>>>>     requirements here for that); or
>>>>
>>>> I'm not following here. What does it mean to fold legacy support under 
>>>> HVMlite? HVMlite doesn't have any legacy hardware, and that's the issue when 
>>>> it comes to using native Linux entry points. Linux might expect some legacy 
>>>> PC hardware to be always present, which is not true for HVMlite.
>>>>
>>>> Could you please clarify this point?
>>>
>>> It seems there is a confusion on terms used. By folding legacy support under
>>> HVMLite I meant folding legacy PV path (classic PV with PV interfaces) under
>>> HVMlite.
>>
>> Ewww.
> 
> Probably a confusion again on terms, by the above I meant to say what you seem
> to be indicating below, which is to keep old PV guest support with PV interfaces
> using a new shiny entry.
> 
> Or are we really going to nuke full support for old PV guests ?

Just to be clear: In this case "support for old PV guests" really means,
"Support for running new versions of Linux in PV mode on old
(non-HVMLite-capable) hypervisors".  And yes, that is the plan: in 5
years' time, if you're still running Xen 4.6, to run a Linux 5.17* guest
you'll have to run it in HVM mode, and you won't be able to use it as a
dom0.  (Xen 6.1 will still support Linux 4.5 running in PV mode, however.)

 -George

* Making up version numbers here, obviously