Re: [PATCH v5 5/6] arm64: mm: Implement 4 levels of translation tables

[Steve Capper]

On Thu, May 01, 2014 at 11:34:16AM +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 Jungseok,
One comment below:

[ ... ]

> diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h
> index bc19101..086112b 100644
> --- a/arch/arm64/include/asm/tlb.h
> +++ b/arch/arm64/include/asm/tlb.h
> @@ -100,6 +100,15 @@ static inline void __pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmdp,
>  }
>  #endif
>  
> +#ifdef CONFIG_ARM64_4_LEVELS
> +static inline void __pud_free_tlb(struct mmu_gather *tlb, pmd_t *pudp,
> +				  unsigned long addr)

The second parameter needs to be a pointer to pud_t ?
(this fires up a warning with STRICT_MM_TYPECHECKS).

With that and Christoffer's feedback about expanding the comments on
create_pud_entry addressed:

Reviewed-by: Steve Capper <steve.capper@xxxxxxxxxx>

Cheers,
-- 
Steve
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