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

From: Steve Capper
Date: Mon Apr 14 2014 - 11:13:59 EST

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In reply to: Jungseok Lee: "Re: [PATCH 7/8] arm64: mm: Implement 4 levels of translation tables"
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On Mon, Apr 14, 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.
>
> References
> ----------
> [1]: Principle of ARM Memory Maps, White Paper, Issue C
>

Hi Jungseok,
I've given this a quick run on the Fast Model with huge pages, and it passed
the libhugetlbfs test suite.

Some comments/suggestions below...

> Signed-off-by: Jungseok Lee <jays.lee@xxxxxxxxxxx>
> Reviewed-by: Sungjinn Chung <sungjinn.chung@xxxxxxxxxxx>
> ---
> arch/arm64/Kconfig | 7 +++++
> arch/arm64/include/asm/page.h | 4 ++-
> arch/arm64/include/asm/pgalloc.h | 20 ++++++++++++++
> arch/arm64/include/asm/pgtable-hwdef.h | 8 ++++--
> arch/arm64/include/asm/pgtable.h | 44 +++++++++++++++++++++++++++++--
> arch/arm64/include/asm/tlb.h | 8 ++++++
> arch/arm64/kernel/head.S | 45 ++++++++++++++++++++++++++++++--
> arch/arm64/kernel/traps.c | 5 ++++
> arch/arm64/mm/fault.c | 1 +
> arch/arm64/mm/mmu.c | 14 +++++++++-
> 10 files changed, 148 insertions(+), 8 deletions(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 431acbc..7f5270b 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -184,12 +184,19 @@ config ARM64_3_LEVELS
> help
> This feature enables 3 levels of translation tables.
>
> +config ARM64_4_LEVELS
> + bool "4 level"
> + depends on ARM64_4K_PAGES
> + help
> + This feature enables 4 levels of translation tables.
> +
> endchoice
>
> config ARM64_VA_BITS
> int "Virtual address space size"
> range 39 39 if ARM64_4K_PAGES && ARM64_3_LEVELS
> range 42 42 if ARM64_64K_PAGES && ARM64_2_LEVELS
> + range 48 48 if ARM64_4K_PAGES && ARM64_4_LEVELS
> help
> This feature is determined by a combination of page size and
> level of translation tables.
> diff --git a/arch/arm64/include/asm/page.h b/arch/arm64/include/asm/page.h
> index 268e53d..83b5289 100644
> --- a/arch/arm64/include/asm/page.h
> +++ b/arch/arm64/include/asm/page.h
> @@ -35,8 +35,10 @@
>
> #ifdef CONFIG_ARM64_2_LEVELS
> #include <asm/pgtable-2level-types.h>
> -#else
> +#elif defined(CONFIG_ARM64_3_LEVELS)
> #include <asm/pgtable-3level-types.h>
> +#else
> +#include <asm/pgtable-4level-types.h>
> #endif
>
> extern void __cpu_clear_user_page(void *p, unsigned long user);
> diff --git a/arch/arm64/include/asm/pgalloc.h b/arch/arm64/include/asm/pgalloc.h
> index 4829837..8d745fa 100644
> --- a/arch/arm64/include/asm/pgalloc.h
> +++ b/arch/arm64/include/asm/pgalloc.h
> @@ -26,6 +26,26 @@
>
> #define check_pgt_cache() do { } while (0)
>
> +#ifdef CONFIG_ARM64_4_LEVELS
> +
> +static inline pud_t *pud_alloc_one(struct mm_struct *mm, unsigned long addr)
> +{
> + return (pud_t *)get_zeroed_page(GFP_KERNEL | __GFP_REPEAT);
> +}
> +
> +static inline void pud_free(struct mm_struct *mm, pud_t *pud)
> +{
> + BUG_ON((unsigned long)pud & (PAGE_SIZE-1));
> + free_page((unsigned long)pud);
> +}
> +
> +static inline void pgd_populate(struct mm_struct *mm, pgd_t *pgd, pud_t *pud)
> +{
> + set_pgd(pgd, __pgd(__pa(pud) | PUD_TYPE_TABLE));

Perhaps instead use PGD_TYPE_TABLE?

> +}
> +
> +#endif /* CONFIG_ARM64_4_LEVELS */
> +
> #ifndef CONFIG_ARM64_2_LEVELS
>
> static inline pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long addr)
> diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
> index 9cd86c6..03ad81b 100644
> --- a/arch/arm64/include/asm/pgtable-hwdef.h
> +++ b/arch/arm64/include/asm/pgtable-hwdef.h
> @@ -18,8 +18,10 @@
>
> #ifdef CONFIG_ARM64_2_LEVELS
> #include <asm/pgtable-2level-hwdef.h>
> -#else
> +#elif defined(CONFIG_ARM64_3_LEVELS)
> #include <asm/pgtable-3level-hwdef.h>
> +#else
> +#include <asm/pgtable-4level-hwdef.h>
> #endif
>
> /*
> @@ -27,7 +29,9 @@
> *
> * Level 1 descriptor (PUD).
> */
> -
> +#ifdef CONFIG_ARM64_4_LEVELS
> +#define PUD_TYPE_TABLE (_AT(pudval_t, 3) << 0)

I would be tempted to instead define:
+#define PGD_TYPE_TABLE (_AT(pgdval_t, 3) << 0)
And have that under "Level 0 descriptor (PGD)". There shouldn't be any
need for an #ifdef block.

> +#endif
> #define PUD_TABLE_BIT (_AT(pgdval_t, 1) << 1)
>
> /*
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index a64ce5e..713811d 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -35,7 +35,11 @@
> * VMALLOC and SPARSEMEM_VMEMMAP ranges.
> */
> #define VMALLOC_START (UL(0xffffffffffffffff) << VA_BITS)
> +#ifndef CONFIG_ARM64_4_LEVELS
> #define VMALLOC_END (PAGE_OFFSET - UL(0x400000000) - SZ_64K)
> +#else
> +#define VMALLOC_END (PAGE_OFFSET - UL(0x40000000000) - SZ_64K)

Can we not compute VMALLOC_END explicitly based on VA bits, rather than have
these constants?

> +#endif
>
> #define vmemmap ((struct page *)(VMALLOC_END + SZ_64K))
>
> @@ -44,12 +48,16 @@
> #ifndef __ASSEMBLY__
> extern void __pte_error(const char *file, int line, unsigned long val);
> extern void __pmd_error(const char *file, int line, unsigned long val);
> +extern void __pud_error(const char *file, int line, unsigned long val);
> extern void __pgd_error(const char *file, int line, unsigned long val);
>
> #define pte_ERROR(pte) __pte_error(__FILE__, __LINE__, pte_val(pte))
> #ifndef CONFIG_ARM64_2_LEVELS
> #define pmd_ERROR(pmd) __pmd_error(__FILE__, __LINE__, pmd_val(pmd))
> #endif
> +#ifdef CONFIG_ARM64_4_LEVELS
> +#define pud_ERROR(pud) __pud_error(__FILE__, __LINE__, pud_val(pud))
> +#endif
> #define pgd_ERROR(pgd) __pgd_error(__FILE__, __LINE__, pgd_val(pgd))
>
> /*
> @@ -344,6 +352,30 @@ static inline pmd_t *pud_page_vaddr(pud_t pud)
>
> #endif /* CONFIG_ARM64_2_LEVELS */
>
> +#ifdef CONFIG_ARM64_4_LEVELS
> +
> +#define pgd_none(pgd) (!pgd_val(pgd))
> +#define pgd_bad(pgd) (!(pgd_val(pgd) & 2))
> +#define pgd_present(pgd) (pgd_val(pgd))
> +
> +static inline void set_pgd(pud_t *pgdp, pud_t pgd)

The types are incorrect, this will generate a compile error if you enable
STRICT_MM_TYPECHECKS.

> +{
> + *pgdp = pgd;
> + dsb();
> +}
> +
> +static inline void pgd_clear(pgd_t *pgdp)
> +{
> + set_pgd(pgdp, __pgd(0));
> +}
> +
> +static inline pud_t *pgd_page_vaddr(pgd_t pgd)
> +{
> + return __va(pgd_val(pgd) & PHYS_MASK & (s32)PAGE_MASK);
> +}
> +
> +#endif /* CONFIG_ARM64_4_LEVELS */
> +
> /* to find an entry in a page-table-directory */
> #define pgd_index(addr) (((addr) >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1))
>
> @@ -352,6 +384,14 @@ static inline pmd_t *pud_page_vaddr(pud_t pud)
> /* to find an entry in a kernel page-table-directory */
> #define pgd_offset_k(addr) pgd_offset(&init_mm, addr)
>
> +#ifdef CONFIG_ARM64_4_LEVELS
> +#define pud_index(addr) (((addr) >> PUD_SHIFT) & (PTRS_PER_PUD - 1))
> +static inline pud_t *pud_offset(pgd_t *pgd, unsigned long addr)
> +{
> + return (pud_t *)pgd_page_vaddr(*pgd) + pud_index(addr);
> +}
> +#endif
> +
> /* Find an entry in the second-level page table.. */
> #ifndef CONFIG_ARM64_2_LEVELS
> #define pmd_index(addr) (((addr) >> PMD_SHIFT) & (PTRS_PER_PMD - 1))
> @@ -380,8 +420,8 @@ static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
> extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
> extern pgd_t idmap_pg_dir[PTRS_PER_PGD];
>
> -#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)

This change also affects <4 levels of paging too?

>
> /*
> * Encode and decode a swap entry:
> diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h
> index df378b2..dedfb04 100644
> --- a/arch/arm64/include/asm/tlb.h
> +++ b/arch/arm64/include/asm/tlb.h
> @@ -99,5 +99,13 @@ 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)
> +{
> + tlb_add_flush(tlb, addr);
> + tlb_remove_page(tlb, virt_to_page(pudp));
> +}
> +#endif
>
> #endif
> 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

A comment above this line needs to also be changed?

> @@ -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)

Again, this affects <4 levels of paging.

>
> .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)
> 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

So we essentially need an extra page for PUD mappings for both the
idmap and swapper mappings. Could the logic of create_pgd_entry be
adapted to call create_pud_entry for 4levels? That way a lot of #ifdefs
can be eliminated.

>
> /*
> * Since the page tables have been populated with non-cacheable
> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> index 0484e81..16d5ee5 100644
> --- a/arch/arm64/kernel/traps.c
> +++ b/arch/arm64/kernel/traps.c
> @@ -336,6 +336,11 @@ void __pmd_error(const char *file, int line, unsigned long val)
> pr_crit("%s:%d: bad pmd %016lx.\n", file, line, val);
> }
>
> +void __pud_error(const char *file, int line, unsigned long val)
> +{
> + pr_crit("%s:%d: bad pud %016lx.\n", file, line, val);
> +}
> +
> void __pgd_error(const char *file, int line, unsigned long val)
> {
> pr_crit("%s:%d: bad pgd %016lx.\n", file, line, val);
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index c23751b..ed4a343 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -61,6 +61,7 @@ void show_pte(struct mm_struct *mm, unsigned long addr)
> break;
>
> pud = pud_offset(pgd, addr);
> + printk(", *pud=%016llx", pud_val(*pud));
> if (pud_none(*pud) || pud_bad(*pud))
> break;
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 6b7e895..321f569 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -222,9 +222,17 @@ static void __init alloc_init_pmd(pud_t *pud, unsigned long addr,
> static void __init alloc_init_pud(pgd_t *pgd, unsigned long addr,
> unsigned long end, unsigned long phys)
> {
> - pud_t *pud = pud_offset(pgd, addr);
> + pud_t *pud;
> unsigned long next;
>
> +#ifdef CONFIG_ARM64_4_LEVELS
> + if (pgd_none(*pgd) || pgd_bad(*pgd)) {
> + pud = early_alloc(PTRS_PER_PUD * sizeof(pud_t));
> + pgd_populate(&init_mm, pgd, pud);
> + }
> +#endif

We don't need this #ifdef block, as pgd_none and pgd_bad should be zero when
we have fewer than 4 levels.

> +
> + pud = pud_offset(pgd, addr);
> do {
> next = pud_addr_end(addr, end);
> alloc_init_pmd(pud, addr, next, phys);
> @@ -274,7 +282,11 @@ static void __init map_mem(void)
> * gives us PGDIR_SIZE memory starting from PHYS_OFFSET (which must be
> * aligned to 2MB as per Documentation/arm64/booting.txt).
> */
> +#ifndef CONFIG_ARM64_4_LEVELS
> limit = PHYS_OFFSET + PGDIR_SIZE;
> +#else
> + limit = PHYS_OFFSET + PUD_SIZE;
> +#endif

I think it would be better to define a constant like MEMBLOCK_INITIAL_LIMIT,
then define that per page level. That way the ifdef block can be avoided and
the intent of the code is a little clearer too.

> memblock_set_current_limit(limit);
>
> /* map all the memory banks */

Cheers,
--
Steve
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