Re: [Xen-devel] HVMLite / PVHv2 - using x86 EFI boot entry

From: "Luis R. Rodriguez" <mcgrof@kernel.org>
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: "Luis R. Rodriguez" <mcgrof@kernel.org>,
	"Roger Pau Monné" <roger.pau@citrix.com>,
	"Matt Fleming" <matt@codeblueprint.co.uk>,
	jeffm@suse.com, "Michael Chang" <MChang@suse.com>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"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>,
	"Juergen Gross" <jgross@suse.com>,
	"Stefano Stabellini" <stefano.stabellini@eu.citrix.com>,
	"Julien Grall" <julien.grall@linaro.org>,
	"George Dunlap" <george.dunlap@citrix.com>,
	joeyli <jlee@suse.com>, "Borislav Petkov" <bp@alien8.de>,
	"Boris Ostrovsky" <boris.ostrovsky@oracle.com>,
	"Charles Arndol" <carnold@suse.com>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"Julien Grall" <julien.grall@arm.com>,
	"Andy Lutomirski" <luto@amacapital.net>,
	"David Vrabel" <david.vrabel@citrix.com>,
	torvalds@linux-foundation.org
Subject: Re: [Xen-devel] HVMLite / PVHv2 - using x86 EFI boot entry
Date: Wed, 13 Apr 2016 21:14:08 +0200	[thread overview]
Message-ID: <20160413191408.GA1990@wotan.suse.de> (raw)
In-Reply-To: <20160413190226.GB7501@char.us.oracle.com>

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 ?

> > I got the impression that if we wanted to remove the old PV path we had to see
> > if we can address old classic PV x86 guests through HVMlite, otherwise we'd
> > have to live with the old PV path for the long term.
> 
> No. We need to deprecate the PV paths - and the agreement we hammered out
> with the x86 maintainers was that once PVH/HVMLite is stable the clock
> would start ticking on PV (pvops) life. All the big users of PV Linux
> were told in persons to prep them for this.

That's nice. *How* that is done is what we are determining here.

> Keep in mind that this is not for deleting of support in hypervisor for
> PV hypercalls - meaning you would still be able to run say 2.6.18 RHEL5
> in years to come. It is just that Linux v6.1 won't have any more PV paths
> and can only run in HVM or PVH/HVMLite mode under Xen.

Sure.

  Luis