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

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Date:	Fri, 15 Apr 2016 17:30:28 +0200
From:	"Luis R. Rodriguez" <mcgrof@...nel.org>
To:	George Dunlap <george.dunlap@...rix.com>
Cc:	"Luis R. Rodriguez" <mcgrof@...nel.org>,
	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 Fri, Apr 15, 2016 at 10:59:16AM +0100, George Dunlap wrote:
> On 14/04/16 20:44, Luis R. Rodriguez wrote:
> > No, I meant to ask, would it be possible to make booting HVMLite using EFI
> > be optional ? That way if you already support EFI that can be used on
> > your entires with some small modifications.
> 
> I wasn't talking about actual non-Linux unikernels; I was talking about using
> Linux in the way that unikernels are used ("unikernel-style").  That is, you
> boot a minimal Linux image with a small ramdisk and have a single process
> running as init.  For this use case, even an extra megabyte of guest RAM and
> an extra second of boot time is a significant cost.  "Use OVMF for domUs" is
> an excellent solution for traditional VMs where you boot a full distro, but
> would impose a significant cost on using Linux in unikernel-style VMs.

Understood.

> Whether a stripped-down EFI support would be sufficiently low memory /
> latency for such workloads is an open question that would take time and
> engineering effort to discover.  And in any case, it would certainly
> require the maintenance of Yet Another Bootloader in the Xen source tree.

OVMF is used by ARM, so using it should be a matter of adaptation, and
some changes other than perhaps DT use. Question still stands though,
would it be possible to have HVMLite be using EFI as an option so that
some users could opt-in if they so wish ?

To be clear, at this point I am not suggesting this be done, just evaluating
the options available.

  Luis