linux-kernel - Re: [PATCH v3 4/6] arm: add early

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Message-ID: <20140116003542.GS15937@n2100.arm.linux.org.uk>
Date:	Thu, 16 Jan 2014 00:35:42 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Laura Abbott <lauraa@...eaurora.org>
Cc:	Mark Salter <msalter@...hat.com>, linux-kernel@...r.kernel.org,
	Arnd Bergmann <arnd@...db.de>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 4/6] arm: add early_ioremap support

On Wed, Jan 15, 2014 at 04:32:03PM -0800, Laura Abbott wrote:
> Neither x86 nor arm64 get rid of existing mapping in paging_init. Is  
> there a reason this needs to be here for arm? Are there concerns about  
> alias mappings?

The early mappings we setup in the assembly code are imperfect - they're
an approximation.  We map just about enough memory to get the kernel
going, and we setup a mapping for the debug stuff using a section
mapping, which may not be appropriate.

The permissions too are a just chosen to get things going, and the
subsequent replacement of the page table entries is to fix all that up.
We really don't want any old entries left behind.

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