linux-kernel - Re: [PATCH v8 09/16] ARM: LPAE: MMU setup for the 3-level page table format

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Date:	Thu, 10 Nov 2011 17:24:58 -0500 (EST)
From:	Nicolas Pitre <nico@...xnic.net>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 09/16] ARM: LPAE: MMU setup for the 3-level page table
 format

On Mon, 7 Nov 2011, Catalin Marinas wrote:

[...]
> +	/*
> +	 * Macro for setting up the TTBRx and TTBCR registers.
> +	 * - \ttbr1 updated.
> +	 */
> +	.macro	v7_ttb_setup, zero, ttbr0, ttbr1, tmp
> +	mrc	p15, 0, \tmp, c2, c0, 2		@ TTB control register
> +	orr	\tmp, \tmp, #TTB_EAE
> +	ALT_SMP(orr	\tmp, \tmp, #TTB_FLAGS_SMP)
> +	ALT_SMP(orr	\tmp, \tmp, #TTB_FLAGS_SMP << 16)
> +	ALT_UP(orr	\tmp, \tmp, #TTB_FLAGS_UP)
> +	ALT_UP(orr	\tmp, \tmp, #TTB_FLAGS_UP << 16)

The ALT_SMP() and ALT_UP() must always be paired and in the right order.  
The above certainly won't produce what you expect on UP.

> +#if PHYS_OFFSET <= PAGE_OFFSET

Please don't use PHYS_OFFSET like a preprocessor macro anymore.  This is 
becoming a global variable these days, and already is for the majority 
of platforms.

> +	 * TTBR0/TTBR1 split (PAGE_OFFSET):
> +	 *   0x40000000: T0SZ = 2, T1SZ = 0 (not used)
> +	 *   0x80000000: T0SZ = 0, T1SZ = 1
> +	 *   0xc0000000: T0SZ = 0, T1SZ = 2
> +	 *
> +	 * Only use this feature if PHYS_OFFSET <= PAGE_OFFSET, otherwise
> +	 * booting secondary CPUs would end up using TTBR1 for the identity
> +	 * mapping set up in TTBR0.
> +	 */
> +	orr	\tmp, \tmp, #(((PAGE_OFFSET >> 30) - 1) << 16) @ TTBCR.T1SZ
> +#if defined CONFIG_VMSPLIT_2G
> +	/* PAGE_OFFSET == 0x80000000, T1SZ == 1 */
> +	add	\ttbr1, \ttbr1, #1 << 4		@ skip two L1 entries
> +#elif defined CONFIG_VMSPLIT_3G
> +	/* PAGE_OFFSET == 0xc0000000, T1SZ == 2 */
> +	add	\ttbr1, \ttbr1, #4096 * (1 + 3)	@ only L2 used, skip pgd+3*pmd
> +#endif
> +#endif	/* PHYS_OFFSET <= PAGE_OFFSET */

What about CONFIG_VMSPLIT_1G ?


Nicolas
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