linux-kernel - Re: [PATCH] x86, efi: Calling __pa() with an ioremap'd address is invalid

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Date:	Tue, 11 Oct 2011 16:58:09 +0100
From:	Matt Fleming <matt@...sole-pimps.org>
To:	"hpanvin@...il.com" <hpa@...or.com>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <ming@...e.hu>, Zhang Rui <rui.zhang@...el.com>,
	Huang Ying <huang.ying.caritas@...il.com>
Subject: Re: [PATCH] x86, efi: Calling __pa() with an ioremap'd address is
 invalid

On Tue, 2011-10-11 at 08:45 -0700, hpanvin@...il.com wrote:
> I think ioremap_cache() should work for either.

Sorry yeah, it will work but I don't think it's desirable (that's what I
meant, though I realise it's not what I wrote).

The reason being: aren't you doing an extra step of indirection because
you have to jump through the vmalloc space?

With 32-bit this is obviously necessary because of the lack of space for
the direct kernel map, but on 64-bit we can just extend the kernel map
and do quick conversions between physical and virtual space with __va()
and __pa().

Maybe the extra indirection isn't that bad and no one will care? If so,
then sure, a unified version sounds like a plan. I was just hesitant of
changing the existing 64-bit implementation for fear of receiving
replies like "you've now made the 64-bit path slower".

-- 
Matt Fleming, Intel Open Source Technology Center

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