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

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Date:	Thu, 14 Apr 2016 10:53:47 +0100
From:	George Dunlap <george.dunlap@...rix.com>
To:	"Luis R. Rodriguez" <mcgrof@...nel.org>
CC:	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>,
	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>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Roger Pau Monné <roger.pau@...rix.com>
Subject: Re: [Xen-devel] HVMLite / PVHv2 - using x86 EFI boot entry

On 13/04/16 20:52, Luis R. Rodriguez wrote:
> On Wed, Apr 13, 2016 at 04:44:54PM +0100, George Dunlap wrote:
>> On Thu, Apr 7, 2016 at 7:51 PM, Luis R. Rodriguez <mcgrof@...e.com> wrote:
>>> So more to it, if the EFI entry already provides a way into Linux
>>> in a more streamlined fashion bringing it closer to the bare metal
>>> boot entry, why *would* we add another boot entry to x86, even if
>>> its small and self contained ?
>>
>> We would avoid using EFI if:
> 
> And this is what I was looking for, thanks!
> 
>> * Being called both on real hardware and under Xen would make the EFI
>> entry point more complicated
> 
> That's on the EFI Linux maintainer to assess. And he seems willing to
> consider this.
> 
>> * Adding the necessary EFI support into Xen would be a significant
>> chunk of extra work
> 
> This seems to be a good sticking point, but Andi noted another aspect
> of this or redundancy as well.
> 
>> * Requiring PVH mode to implement EFI would make it more difficult for
>> other kernes (NetBSD, FreeBSD) to act as dom0s.
> 
> What if this is an option only then ?
> 
>>
>> * Requiring PVH mode to use EFI would make it more difficult to
>> support unikernel-style workloads for domUs.
> 
> What if this is an option only then ?

So first of all, you asked why anyone would oppose EFI, and this is part
of the answer to that.

Secondly, you mean "What if this is the only thing the Linux maintainers
will accept?"  And you already know the answer to that.

How much of a burden it would be on the rest of the open-source
ecosystem (Xen, *BSDs, &c) is a combination of some as-yet unknown facts
(i.e., what a minimal Xen/Linux EFI interface would look like) and a
matter of judgement (i.e., given the same interface, reasonable people
may come to different conclusions about whether the interface is an
undue burden to impose on others or not).

But I would hope that the Linux maintainers would at least consider the
broader community when weighing their decisions, and not take advantage
of their position of dominance to simply ignore the effect of their
choices on everybody else.

 -George