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

[Jungseok Lee <jays.lee@samsung.com>]

On Tuesday, May 06, 2014 9:02 PM, Steve Capper wrote:
> 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:

Hi Steve.

> [ ... ]
> 
> > 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).

You're right. My fault...

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

Okay. I will add it.

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

Thanks for review!

- Jungseok Lee