linux-kernel - Re: [PATCH] [RESEND] arm: limit memblock base address for early_pte

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Date:	Thu, 28 Jun 2012 13:50:16 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
cc:	Dave Martin <dave.martin@...aro.org>,
	Minchan Kim <minchan@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Chanho Min <chanho.min@....com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Jongsung Kim <neidhard.kim@....com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] [RESEND] arm: limit memblock base address for
 early_pte_alloc

On Thu, 28 Jun 2012, Russell King - ARM Linux wrote:

> Err, I don't think you understand what's going on here.
> 
> The sequence is:
> 
> 1. setup the initial mappings so we can run the kernel in virtual space.
> 2. provide the memory areas to memblock
> 3. ask the platform to reserve whatever memory it wants from memblock
>    [this means using memblock_reserve or arm_memblock_steal).  The
>    reserved memory is *not* expected to be mapped at this point, and is
>    therefore inaccessible.
> 4. Setup the lowmem mappings.

I do understand that pretty well so far.

> And when we're setting up the lowmem mappings, we do *not* expect to
> create any non-section page mappings, which again means we have no reason
> to use the memblock allocator to obtain memory that we want to immediately
> use.

And why does this have to remain so?

> So I don't know where you're claim of being "fragile" is coming from.

It doesn't come from anything you've described so far. It comes from 
those previous attempts at lifting this limitation.  I think that my 
proposal is much less fragile than the other ones.

> What is fragile is people wanting to use arm_memblock_steal() without
> following the rules for it I layed down.

What about enhancing your rules if the technical limitations they were 
based on are lifted?


Nicolas
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