Re: [PATCH 02/14] arm64: Handle section maps for swapper/idmap

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 13 August 2015 at 13:33, Suzuki K. Poulose <suzuki.poulose@arm.com> wrote:
> From: "Suzuki K. Poulose" <suzuki.poulose@arm.com>
>
> We use section maps with 4K page size to create the
> swapper/idmaps. So far we have used !64K or 4K checks
> to handle the case where we use the section maps. This
> patch adds a symbol to make it clear those cases.
>

That sentence does not make sense.

> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Signed-off-by: Suzuki K. Poulose <suzuki.poulose@arm.com>
> ---
>  arch/arm64/include/asm/kernel-pgtable.h |   31 +++++++++-----
>  arch/arm64/mm/mmu.c                     |   70 ++++++++++++++-----------------
>  2 files changed, 51 insertions(+), 50 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kernel-pgtable.h b/arch/arm64/include/asm/kernel-pgtable.h
> index 622929d..5876a36 100644
> --- a/arch/arm64/include/asm/kernel-pgtable.h
> +++ b/arch/arm64/include/asm/kernel-pgtable.h
> @@ -19,6 +19,13 @@
>  #ifndef __ASM_KERNEL_PGTABLE_H
>  #define __ASM_KERNEL_PGTABLE_H
>
> +/* With 4K pages, we use section maps. */
> +#ifdef CONFIG_ARM64_4K_PAGES
> +#define ARM64_SWAPPER_USES_SECTION_MAPS 1
> +#else
> +#define ARM64_SWAPPER_USES_SECTION_MAPS 0
> +#endif
> +
>  /*
>   * The idmap and swapper page tables need some space reserved in the kernel
>   * image. Both require pgd, pud (4 levels only) and pmd tables to (section)
> @@ -28,26 +35,28 @@
>   * could be increased on the fly if system RAM is out of reach for the default
>   * VA range, so 3 pages are reserved in all cases.
>   */
> -#ifdef CONFIG_ARM64_64K_PAGES
> -#define SWAPPER_PGTABLE_LEVELS (CONFIG_PGTABLE_LEVELS)
> -#else
> +#if ARM64_SWAPPER_USES_SECTION_MAPS
>  #define SWAPPER_PGTABLE_LEVELS (CONFIG_PGTABLE_LEVELS - 1)
> +#else
> +#define SWAPPER_PGTABLE_LEVELS (CONFIG_PGTABLE_LEVELS)
>  #endif
>
>  #define SWAPPER_DIR_SIZE       (SWAPPER_PGTABLE_LEVELS * PAGE_SIZE)
>  #define IDMAP_DIR_SIZE         (3 * PAGE_SIZE)
>
>  /* Initial memory map size */
> -#ifdef CONFIG_ARM64_64K_PAGES
> -#define SWAPPER_BLOCK_SHIFT    PAGE_SHIFT
> -#define SWAPPER_BLOCK_SIZE     PAGE_SIZE
> -#define SWAPPER_TABLE_SHIFT    PMD_SHIFT
> -#else
> +#if ARM64_SWAPPER_USES_SECTION_MAPS
>  #define SWAPPER_BLOCK_SHIFT    SECTION_SHIFT
>  #define SWAPPER_BLOCK_SIZE     SECTION_SIZE
>  #define SWAPPER_TABLE_SHIFT    PUD_SHIFT
> +#else
> +#define SWAPPER_BLOCK_SHIFT    PAGE_SHIFT
> +#define SWAPPER_BLOCK_SIZE     PAGE_SIZE
> +#define SWAPPER_TABLE_SHIFT    PMD_SHIFT
>  #endif
>
> +/* The size of the initial kernel direct mapping */
> +#define SWAPPER_INIT_MAP_SIZE  (_AC(1, UL) << SWAPPER_TABLE_SHIFT)
>
>  /*
>   * Initial memory map attributes.
> @@ -55,10 +64,10 @@
>  #define SWAPPER_PTE_FLAGS      PTE_TYPE_PAGE | PTE_AF | PTE_SHARED
>  #define SWAPPER_PMD_FLAGS      PMD_TYPE_SECT | PMD_SECT_AF | PMD_SECT_S
>
> -#ifdef CONFIG_ARM64_64K_PAGES
> -#define SWAPPER_MM_MMUFLAGS    PTE_ATTRINDX(MT_NORMAL) | SWAPPER_PTE_FLAGS
> -#else
> +#if ARM64_SWAPPER_USES_SECTION_MAPS
>  #define SWAPPER_MM_MMUFLAGS    PMD_ATTRINDX(MT_NORMAL) | SWAPPER_PMD_FLAGS
> +#else
> +#define SWAPPER_MM_MMUFLAGS    PTE_ATTRINDX(MT_NORMAL) | SWAPPER_PTE_FLAGS
>  #endif
>
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 9211b85..71230488 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -32,6 +32,7 @@
>
>  #include <asm/cputype.h>
>  #include <asm/fixmap.h>
> +#include <asm/kernel-pgtable.h>
>  #include <asm/sections.h>
>  #include <asm/setup.h>
>  #include <asm/sizes.h>
> @@ -353,14 +354,11 @@ static void __init map_mem(void)
>          * memory addressable from the initial direct kernel mapping.
>          *
>          * The initial direct kernel mapping, located at swapper_pg_dir, gives
> -        * us PUD_SIZE (4K pages) or PMD_SIZE (64K pages) memory starting from
> -        * PHYS_OFFSET (which must be aligned to 2MB as per
> -        * Documentation/arm64/booting.txt).
> +        * us PUD_SIZE (with SECTION maps, i.e, 4K) or PMD_SIZE (without
> +        * SECTION maps, i.e, 64K pages) memory starting from PHYS_OFFSET
> +        * (which must be aligned to 2MB as per Documentation/arm64/booting.txt).
>          */
> -       if (IS_ENABLED(CONFIG_ARM64_64K_PAGES))
> -               limit = PHYS_OFFSET + PMD_SIZE;
> -       else
> -               limit = PHYS_OFFSET + PUD_SIZE;
> +       limit = PHYS_OFFSET + SWAPPER_INIT_MAP_SIZE;
>         memblock_set_current_limit(limit);
>
>         /* map all the memory banks */
> @@ -371,21 +369,24 @@ static void __init map_mem(void)
>                 if (start >= end)
>                         break;
>
> -#ifndef CONFIG_ARM64_64K_PAGES
> -               /*
> -                * For the first memory bank align the start address and
> -                * current memblock limit to prevent create_mapping() from
> -                * allocating pte page tables from unmapped memory.
> -                * When 64K pages are enabled, the pte page table for the
> -                * first PGDIR_SIZE is already present in swapper_pg_dir.
> -                */
> -               if (start < limit)
> -                       start = ALIGN(start, PMD_SIZE);
> -               if (end < limit) {
> -                       limit = end & PMD_MASK;
> -                       memblock_set_current_limit(limit);
> +               if (ARM64_SWAPPER_USES_SECTION_MAPS) {
> +                       /*
> +                        * For the first memory bank align the start address and
> +                        * current memblock limit to prevent create_mapping() from
> +                        * allocating pte page tables from unmapped memory. With
> +                        * the section maps, if the first block doesn't end on section
> +                        * size boundary, create_mapping() will try to allocate a pte
> +                        * page, which may be returned from an unmapped area.
> +                        * When section maps are not used, the pte page table for the
> +                        * current limit is already present in swapper_pg_dir.
> +                        */
> +                       if (start < limit)
> +                               start = ALIGN(start, SECTION_SIZE);
> +                       if (end < limit) {
> +                               limit = end & SECTION_MASK;
> +                               memblock_set_current_limit(limit);
> +                       }
>                 }
> -#endif
>                 __map_memblock(start, end);
>         }
>
> @@ -638,7 +639,7 @@ void *__init fixmap_remap_fdt(phys_addr_t dt_phys)
>  {
>         const u64 dt_virt_base = __fix_to_virt(FIX_FDT);
>         pgprot_t prot = PAGE_KERNEL | PTE_RDONLY;
> -       int granularity, size, offset;
> +       int size, offset;
>         void *dt_virt;
>
>         /*
> @@ -664,24 +665,15 @@ void *__init fixmap_remap_fdt(phys_addr_t dt_phys)
>          */
>         BUILD_BUG_ON(dt_virt_base % SZ_2M);
>
> -       if (IS_ENABLED(CONFIG_ARM64_64K_PAGES)) {
> -               BUILD_BUG_ON(__fix_to_virt(FIX_FDT_END) >> PMD_SHIFT !=
> -                            __fix_to_virt(FIX_BTMAP_BEGIN) >> PMD_SHIFT);
> -
> -               granularity = PAGE_SIZE;
> -       } else {
> -               BUILD_BUG_ON(__fix_to_virt(FIX_FDT_END) >> PUD_SHIFT !=
> -                            __fix_to_virt(FIX_BTMAP_BEGIN) >> PUD_SHIFT);
> -
> -               granularity = PMD_SIZE;
> -       }
> +       BUILD_BUG_ON(__fix_to_virt(FIX_FDT_END) >> SWAPPER_TABLE_SHIFT !=
> +                    __fix_to_virt(FIX_BTMAP_BEGIN) >> SWAPPER_TABLE_SHIFT);
>
> -       offset = dt_phys % granularity;
> +       offset = dt_phys % SWAPPER_BLOCK_SIZE;
>         dt_virt = (void *)dt_virt_base + offset;
>
>         /* map the first chunk so we can read the size from the header */
> -       create_mapping(round_down(dt_phys, granularity), dt_virt_base,
> -                      granularity, prot);
> +       create_mapping(round_down(dt_phys, SWAPPER_BLOCK_SIZE), dt_virt_base,
> +                      SWAPPER_BLOCK_SIZE, prot);
>
>         if (fdt_check_header(dt_virt) != 0)
>                 return NULL;
> @@ -690,9 +682,9 @@ void *__init fixmap_remap_fdt(phys_addr_t dt_phys)
>         if (size > MAX_FDT_SIZE)
>                 return NULL;
>
> -       if (offset + size > granularity)
> -               create_mapping(round_down(dt_phys, granularity), dt_virt_base,
> -                              round_up(offset + size, granularity), prot);
> +       if (offset + size > SWAPPER_BLOCK_SIZE)
> +               create_mapping(round_down(dt_phys, SWAPPER_BLOCK_SIZE), dt_virt_base,
> +                              round_up(offset + size, SWAPPER_BLOCK_SIZE), prot);
>
>         memblock_reserve(dt_phys, size);
>
> --
> 1.7.9.5
>