linux-kernel - Re: [PATCH v4 06/12] efi: export efi runtime memory mapping to sysfs

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Message-ID: <20131129115029.GB4266@pd.tnic>
Date:	Fri, 29 Nov 2013 12:50:29 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Dave Young <dyoung@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
	x86@...nel.org, mjg59@...f.ucam.org, hpa@...or.com,
	James.Bottomley@...senPartnership.com, vgoyal@...hat.com,
	ebiederm@...ssion.com, horms@...ge.net.au,
	kexec@...ts.infradead.org, greg@...ah.com, matt@...sole-pimps.org,
	toshi.kani@...com
Subject: Re: [PATCH v4 06/12] efi: export efi runtime memory mapping to sysfs

On Fri, Nov 29, 2013 at 05:40:35PM +0800, Dave Young wrote:
> Matt are suggesting to below one, is it ok to you? I'm fine with both.
>
> The efi runtime services can only be switched to virtual mode once
> without rebooting. The kexec kernel must maintain the same physical
> to virtual address mappings as the first kernel. The mappings are
> exported to sysfs so userspace tools can reassemble them and pass them
> into the kexec kernel.

His is explaining it better so take his :)

> Is it always 4K, how about "in pages"?

Actually no, so "in pages" is better.

> Since we do not know the exact number of ranges, introducing a list
> or count the totoal range numbers before will add more code. Do you
> really think it's necessary?
>
> I tend to not fix every warnings from checkpatch if it's not a
> must-fix one.

No need for the list - I actually meant you simply use a tmp pointer for
each krealloc invocation - just look around the tree for examples.

Also think about what happens to the pointed-to memory when krealloc
returns NULL.

> suppose kexec runtime map preparing fails we still can get 1st kernel
> boot ok.

Yeah, nothing stops that - especially if you iterate over the mapped
regions a second time separately, for kexec.

Which reminds me, all that save_runtime_map code needs to be behind
CONFIG_KEXEC. We don't want to be doing this if KEXEC is not enabled.

> > What would be much cleaner IMO would be if you let efi_map_regions()
> > finish, *and*, *only* if it was successful iterate again over the
> > regions and do efi_save_runtime_map() on the runtime ones. This will
> > make the code much more readable too.
> 
> For simplifying the code, will do.

Right, and hide it behind CONFIG_KEXEC too, while you're at it.

> I did not add KEXEC because I thought it can be used for debugging
> purpose.

mfleming is thinking about it :)

> Will check and update, what tree are you using?

Always current Linus tree and tip/master. This helps catch issues like
that.

> Hmm, it's created in efi.c so I think we can not move it..

Ok, so we apparently export naked kobjects like that. All right, fair
enough.

...

> Thanks for catching, actually I have changed it in my local tree since
> your last comment about other file.

:)

Thanks.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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