linux-kernel - Re: [PATCH] x86, boot: Allow 64bit EFI kernel to be loaded above 4G

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Message-ID: <20150211155524.GC4665@codeblueprint.co.uk>
Date:	Wed, 11 Feb 2015 15:55:24 +0000
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Jonathan Corbet <corbet@....net>,
	Kees Cook <keescook@...omium.org>,
	Junjie Mao <eternal.n08@...il.com>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Peter Jones <pjones@...hat.com>
Subject: Re: [PATCH] x86, boot: Allow 64bit EFI kernel to be loaded above 4G

On Mon, 09 Feb, at 12:23:15PM, Yinghai Lu wrote:
> On Mon, Feb 9, 2015 at 10:27 AM, Matt Fleming <matt@...eblueprint.co.uk> wrote:
> > On Tue, 03 Feb, at 06:03:20PM, Yinghai Lu wrote:
> >
> > The first thing that comes to mind is the issues we experienced last
> > year when adding support for loading initrds above 4GB to the EFI boot
> > stub, c.f. commit 47226ad4f4cf ("x86/efi: Only load initrd above 4g on
> > second try").
> >
> > Are things going to work correctly this time?
> 
> That should be addressed the grub2.
 
I vaguely remember thinking that the issue was only experienced when
using the EFI_FILE protocol, which grub2 doesn't use. So the grub
developers may be OK, but we should at least give them a heads up.

> I was thinking that we may need to add mem_limit command together with
> linuxefi and initrdefi.
> or add linuxefi64/initrdefi64?
 
No, we definitely do not want to add any more grub commands.

> BTW, I tested loading kernel above grub2 on
> virutalbox, qemu/kvm/OVMF, and real servers (ami ...) all work without problem.
> 
> wonder if we need have one black list for 64bit UEFI that does not
> support access
> memory above 4G.
 
We have been successful, so far, in not introducing these kind of
blacklists. It would be a shame to start now.

-- 
Matt Fleming, Intel Open Source Technology Center
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