linux-kernel - Re: RFC: default CONFIG_EFI

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Date:	Tue, 13 Aug 2013 11:52:04 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
CC:	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Matt Fleming <matt.fleming@...el.com>
Subject: Re: RFC: default CONFIG_EFI_STUB=y

On 08/13/2013 11:43 AM, James Bottomley wrote:
>> James, does this address your concerns?
> 
> You mean for globally enabling CONFIG_EFI on x86?  not really for 32
> bit, you say above it's pretty much unusable; I'd prefer just to enable
> it for 64 bit.  As you said in your original post "since EFI now is a
> significant percentage of all systems" but you actually mean EFI64 ...
> EFI32 is a pretty insignificant percentage of all systems.

For better or worse, there will be more.

> Can we actually boot a 32 bit kernel on an EFI64 system?  The last time
> I tried on my Secure Boot SDV it wouldn't work; the problem is getting
> someting in the transfer of control path to boot the processor back to
> 32 bit mode.

We can boot with a bootloader in "skip stub" mode; no runtime services
yet.  We are working on making it possible to boot via a EFI stub in
assisted mode (still needing a bootloader, but with the boot stub in the
kernel.)

Runtime services will be the last piece, obviously, but even that looks
reasonably doable.

	-hpa

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