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SubjectRe: [regression, bisected] x86: efi: Pass boot services variable info to runtime code
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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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