linux-kernel - Re: [PATCH v2][EFI] Run EFI in physical mode

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Date:	Thu, 13 Jan 2011 17:41:39 +0000
From:	Matthew Garrett <mjg@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Takao Indoh <indou.takao@...fujitsu.com>,
	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	horms@...ge.net.au, nhorman@...driver.com,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	mingo@...hat.com, hpa@...or.com, tglx@...utronix.de,
	vgoyal@...hat.com
Subject: Re: [PATCH v2][EFI] Run EFI in physical mode

On Thu, Jan 13, 2011 at 09:16:26AM -0800, Eric W. Biederman wrote:
> Matthew Garrett <mjg@...hat.com> writes:
> 
> > We're seeing issues with some Dell hardware when EFI is run in physical 
> > mode - it seems that Windows uses virtual mode, so the physical path is 
> > never exercised. I'm not sure that changing the default to physical is 
> > going to be possible without compatibility issues.
> 
> The bootloaders use physical mode, and there shouldn't be a separate
> physical vs virtual mode.  It should be the same code with or without
> relocations applied.  At worst we can set virtual address to the
> physical address, on buggy boards.

Haven't we learned that failing to mimic Windows as closely as possible 
in firmware interactions is a recipe for immense disaster yet? We'll 
never successfully blacklist every broken machine.

> Honestly if the problem is the EFI code is so buggy we can't use it
> in physical mode the answer is almost certainly not to use the
> buggy EFI code.

Which would be fine, except...

> The only bits that I don't think have an alternative are the firmware
> variable accesses.   Which are a nice to have, but not a show stopper
> anywhere.

It's not typically possible to set up the bootloader without EFI 
variable acccess.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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