linux-kernel - Re: [PATCH 7/8] arm64: mm: Implement 4 levels of translation tables

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Message-ID: <20140414091424.GA14204@linaro.org>
Date:	Mon, 14 Apr 2014 10:14:25 +0100
From:	Steve Capper <steve.capper@...aro.org>
To:	Jungseok Lee <jays.lee@...sung.com>
Cc:	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
	Catalin.Marinas@....com, Marc Zyngier <Marc.Zyngier@....com>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	kgene.kim@...sung.com, Arnd Bergmann <arnd@...db.de>,
	linux-kernel@...r.kernel.org, ilho215.lee@...sung.com,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	sungjinn.chung@...sung.com
Subject: Re: [PATCH 7/8] arm64: mm: Implement 4 levels of translation tables

On Mon, Apr 13, 2014 at 04:41:07PM +0900, Jungseok Lee wrote:
> This patch implements 4 levels of translation tables since 3 levels
> of page tables with 4KB pages cannot support 40-bit physical address
> space described in [1] due to the following issue.
> 
> It is a restriction that kernel logical memory map with 4KB + 3 levels
> (0xffffffc000000000-0xffffffffffffffff) cannot cover RAM region from
> 544GB to 1024GB in [1]. Specifically, ARM64 kernel fails to create
> mapping for this region in map_mem function since __phys_to_virt for
> this region reaches to address overflow.
> 
> If SoC design follows the document, [1], over 32GB RAM would be placed
> from 544GB. Even 64GB system is supposed to use the region from 544GB
> to 576GB for only 32GB RAM. Naturally, it would reach to enable 4 levels
> of page tables to avoid hacking __virt_to_phys and __phys_to_virt.
> 
> However, it is recommended 4 levels of page table should be only enabled
> if memory map is too sparse or there is about 512GB RAM.

Hi,
So I thought I'd apply this series and have a play, this patch doesn't apply
cleanly for me, please see below why...

[ ... ]

> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index 0fd5650..0b0b16a 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -46,8 +46,8 @@
>  #error KERNEL_RAM_VADDR must start at 0xXXX80000
>  #endif
>  
> -#define SWAPPER_DIR_SIZE	(3 * PAGE_SIZE)
> -#define IDMAP_DIR_SIZE		(2 * PAGE_SIZE)
> +#define SWAPPER_DIR_SIZE	(4 * PAGE_SIZE)
> +#define IDMAP_DIR_SIZE		(3 * PAGE_SIZE)
>  
>  	.globl	swapper_pg_dir
>  	.equ	swapper_pg_dir, KERNEL_RAM_VADDR - SWAPPER_DIR_SIZE
> @@ -384,6 +384,20 @@ ENDPROC(__calc_phys_offset)
>  	.endm
>  
>  /*
> + * Macro to populate the PUD for the corresponding block entry in the next
> + * level (tbl) for the given virtual address.
> + *
> + * Preserves:	pud, tbl, virt
> + * Corrupts:	tmp1, tmp2
> + */
> +	.macro create_pud_entry, pud, tbl, virt, tmp1, tmp2
> +	lsr	\tmp1, \virt, #PUD_SHIFT
> +	and	\tmp1, \tmp1, #PTRS_PER_PUD - 1	// PUD index
> +	orr	\tmp2, \tbl, #3			// PUD entry table type
> +	str	\tmp2, [\pud, \tmp1, lsl #3]
> +	.endm
> +
> +/*
>   * Macro to populate block entries in the page table for the start..end
>   * virtual range (inclusive).
>   *
> @@ -445,10 +459,18 @@ __create_page_tables:
>  	ldr	x3, =KERNEL_START
>  	add	x3, x3, x28			// __pa(KERNEL_START)

I don't think we have C++ style comments in the kernel. Also, I can't see
any references to =KERNEL_START in arch/arm64/kernel/head.S (from 3.14 down).

>  	create_pgd_entry x25, x0, x3, x5, x6
> +#ifdef CONFIG_ARM64_4_LEVELS
> +	add	x1, x0, #PAGE_SIZE
> +	create_pud_entry x0, x1, x3, x5, x6
> +#endif
>  	ldr	x6, =KERNEL_END
>  	mov	x5, x3				// __pa(KERNEL_START)
>  	add	x6, x6, x28			// __pa(KERNEL_END)
> +#ifndef CONFIG_ARM64_4_LEVELS
>  	create_block_map x0, x7, x3, x5, x6
> +#else
> +	create_block_map x1, x7, x3, x5, x6
> +#endif
>  
>  	/*
>  	 * Map the kernel image (starting with PHYS_OFFSET).
> @@ -456,9 +478,17 @@ __create_page_tables:
>  	add	x0, x26, #PAGE_SIZE		// section table address
>  	mov	x5, #PAGE_OFFSET
>  	create_pgd_entry x26, x0, x5, x3, x6
> +#ifdef CONFIG_ARM64_4_LEVELS
> +	add	x1, x0, #PAGE_SIZE
> +	create_pud_entry x0, x1, x3, x5, x6
> +#endif
>  	ldr	x6, =KERNEL_END
>  	mov	x3, x24				// phys offset
> +#ifndef CONFIG_ARM64_4_LEVELS
>  	create_block_map x0, x7, x3, x5, x6
> +#else
> +	create_block_map x1, x7, x3, x5, x6
> +#endif
>  
>  	/*
>  	 * Map the FDT blob (maximum 2MB; must be within 512MB of
> @@ -474,14 +504,25 @@ __create_page_tables:
>  	add	x5, x5, x6			// __va(FDT blob)
>  	add	x6, x5, #1 << 21		// 2MB for the FDT blob
>  	sub	x6, x6, #1			// inclusive range
> +#ifndef CONFIG_ARM64_4_LEVELS
>  	create_block_map x0, x7, x3, x5, x6
> +#else
> +	create_block_map x1, x7, x3, x5, x6
> +#endif
>  1:
>  	/*
>  	 * Create the pgd entry for the fixed mappings.
>  	 */
>  	ldr	x5, =FIXADDR_TOP		// Fixed mapping virtual address
> +#ifndef CONFIG_ARM64_4_LEVELS
>  	add	x0, x26, #2 * PAGE_SIZE		// section table address
>  	create_pgd_entry x26, x0, x5, x6, x7
> +#else
> +	add	x0, x26, #PAGE_SIZE
> +	create_pgd_entry x26, x0, x5, x6, x7
> +	add	x1, x0, #2 * PAGE_SIZE
> +	create_pud_entry x0, x1, x5, x6, x7
> +#endif
>  
>  	/*
>  	 * Since the page tables have been populated with non-cacheable

What tree is this series based on?

Thanks,
-- 
Steve
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