linux-kernel - Re: [RFC PATCH 06/18] ARM: LPAE: Introduce the 3-level page table format definitions

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Message-Id: <201010251315.53304.arnd@arndb.de>
Date:	Mon, 25 Oct 2010 13:15:53 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 06/18] ARM: LPAE: Introduce the 3-level page table format definitions

On Monday 25 October 2010, Catalin Marinas wrote:
> +/*
> + * With LPAE, there are 3 levels of page tables. Each level has 512 entries of
> + * 8 bytes each, occupying a 4K page. The first level table covers a range of
> + * 512GB, each entry representing 1GB. Since we are limited to 4GB input
> + * address range, only 4 entries in the PGD are used.
> + *
> + * There are enough spare bits in a page table entry for the kernel specific
> + * state.
> + */
> +#define PTRS_PER_PTE           512
> +#define PTRS_PER_PMD           512
> +#define PTRS_PER_PGD           4

Since the PGD is so extremely small, would it be possible to fold it
into the mm_context_t in order to save an allocation?
Or does the PGD still require page alignment?

Do you also have patches to allow 40-bit virtual space? I suppose we
will need that for KVM support in the future.

	Arnd

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