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

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Date:	Thu, 12 Feb 2015 14:59:42 +0000
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Peter Jones <pjones@...hat.com>
Cc:	Yinghai Lu <yinghai@...nel.org>,
	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>
Subject: Re: [PATCH] x86, boot: Allow 64bit EFI kernel to be loaded above 4G

On Wed, 11 Feb, at 11:29:58AM, Peter Jones wrote:
> 
> From grub's point of view I'm not sure why we'd care - the pages kernel
> and initramfs land in are both from the Boot Services allocator, so if the
> machine doesn't support high addresses, they won't be there.

It's not that some implementations don't "support" higher addresses,
it's that the EFI_FILE_PROTOCOL is buggy and it corrupts the memory when
reading into it; you can allocate it just fine. At least, that's what I
remember from the limited investigation I performed.

But since grub doesn't use EFI_FILE_PROTOCOL, we should be cool.

-- 
Matt Fleming, Intel Open Source Technology Center
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