linux-kernel - Re: [regression, bisected] x86: efi: Pass boot services variable info to runtime code

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Date:	Fri, 31 May 2013 10:35:32 -0700
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Matthew Garrett <mjg59@...f.ucam.org>
Cc:	Russ Anderson <rja@....com>, Ingo Molnar <mingo@...nel.org>,
	Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>,
	joeyli <jlee@...e.com>, Matt Fleming <matt@...sole-pimps.org>,
	matt.fleming@...el.com, linux-efi@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [regression, bisected] x86: efi: Pass boot services variable
 info to runtime code

On Fri, 2013-05-31 at 17:28 +0100, Matthew Garrett wrote:
> On Fri, May 31, 2013 at 10:43:49AM -0500, Russ Anderson wrote:
> 
> > When did writing EFI variables to nvram become necessary to boot on 
> > UEFI? And if it is necessary, why is it that only linux boot loaders 
> > that use EFI stubs (generally grub2) need it?  The current kernel 
> > boots using EFI/grub and EFI/elilo.  It is just when EFI stubs are 
> > used that the boot fails.
> 
> I think you've misunderstood the problem. If nvram becaomes full, some 
> systems crash during firmware initialisation. So we can't let nvram 
> become full. The obvious thing to do here is to look at the values from 
> QueryVariableInfo, but many systems won't perform any garbage collection 
> until they're almost out of space and so variables that have been 
> deleted still show up as used space. We can work around that by adding 
> up the size of the variables ourselves, but that only gives us the value 
> for runtime-visible variables. We also need to know how much space is 
> used by variables that are only visible during boot, hence calling 
> QueryVariableInfo before ExitBootServices.
> 
> > Which means the previous patch(es) that caused the bricking should
> > get pulled, too.
> 
> There are no patches that cause the bricking.

This is the description of the original problem:

http://www.h-online.com/open/news/item/Booting-Linux-using-UEFI-can-brick-Samsung-laptops-1793958.html

And the further investigation:

http://mjg59.dreamwidth.org/22855.html

If you read the latter, it shows you why we have to use
QueryVariableInfo to try to work out how much space we have available.

James


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