Re: HVMLite / PVHv2 - using x86 EFI boot entry

From: George Dunlap <george.dunlap@citrix.com>
To: "Luis R. Rodriguez" <mcgrof@kernel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: "Matt Fleming" <matt@codeblueprint.co.uk>,
	jeffm@suse.com, "Michael Chang" <MChang@suse.com>,
	"Jim Fehlig" <jfehlig@suse.com>,
	"Jan Beulich" <JBeulich@suse.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"Daniel Kiper" <daniel.kiper@oracle.com>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	"Takashi Iwai" <tiwai@suse.de>,
	"Vojtěch Pavlík" <vojtech@suse.cz>, "Gary Lin" <GLin@suse.com>,
	xen-devel <xen-devel@lists.xenproject.org>,
	"Jeffrey Cheung" <JCheung@suse.com>,
	"Charles Arndol" <carnold@suse.com>,
	"Julien Grall" <julien.grall@arm.com>,
	"Stefano Stabellini" <stefano.stabellini@eu.citrix.com>,
	"Julien Grall" <julien.grall@linaro.org>, joeyli <jlee@suse.com>,
	"Borislav Petkov" <bp@alien8.de>,
	"Boris Ostrovsky" <boris.ostrovsky@oracle.com>,
	"Juergen Gross" <jgross@suse.com>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>
Subject: Re: HVMLite / PVHv2 - using x86 EFI boot entry
Date: Thu, 14 Apr 2016 11:13:49 +0100	[thread overview]
Message-ID: <570F6D5D.60700__10047.3704202615$1460628923$gmane$org@citrix.com> (raw)
In-Reply-To: <20160413191408.GA1990@wotan.suse.de>

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

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