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

Jungseok Lee
2014-04-14T09:25:01Z

On Monday, April 14, 2014 6:14 PM, Steve Capper wrote:
> 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...

This pathset is based on 3.15-rc1.

> [ ... ]
>
> > 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).

C++ style comments are prevalent in arch/arm64/kernel/head.S. I've followed the
code style written previously.

You can see this change in the commit, ea8c2e1124457f266f82effc3e6558552527943a).
It's title is "arm64: Extend the idmap to the whole kernel image".

> > 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?

This series is based on 3.15-rc1.

Thanks
Jungseok Lee