linux-kernel - Re: [PATCH 10/36] AArch64: MMU definitions

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Message-ID: <506A3898.7000804@jonmasters.org>
Date:	Mon, 01 Oct 2012 20:43:04 -0400
From:	Jon Masters <jonathan@...masters.org>
To:	Catalin Marinas <catalin.marinas@....com>
CC:	linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	Will Deacon <will.deacon@....com>
Subject: Re: [PATCH 10/36] AArch64: MMU definitions

On 07/06/2012 05:05 PM, Catalin Marinas wrote:

> +/*
> + * PAGE_OFFSET - the virtual address of the start of the kernel image.
> + * VA_BITS - the maximum number of bits for virtual addresses.
> + * TASK_SIZE - the maximum size of a user space task.
> + * TASK_UNMAPPED_BASE - the lower boundary of the mmap VM area.
> + * The module space lives between the addresses given by TASK_SIZE
> + * and PAGE_OFFSET - it must be within 128MB of the kernel text.
> + */
> +#define PAGE_OFFSET		UL(0xffffffc000000000)
> +#define MODULES_END		(PAGE_OFFSET)
> +#define MODULES_VADDR		(MODULES_END - SZ_64M)
> +#define VA_BITS			(39)
> +#define TASK_SIZE_64		(UL(1) << VA_BITS)

Pedantic nit pick. Shouldn't that "it must be within 128MB of the kernel
text" be "within 128MB of the *end* of the kernel text"? The point being
that on AArch64 unconditional branches are encoded as imm26+1 (27 bits)
and so you're going with -64MB to ensure that you're within the range.

Jon.

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