Re: [PATCH 1/2] x86/mm/ident_map: Add PUD level 1GB page support

[Yinghai Lu]

On Tue, Apr 25, 2017 at 2:13 AM, Xunlei Pang <xlpang@xxxxxxxxxx> wrote:
> The current kernel_ident_mapping_init() creates the identity
> mapping using 2MB page(PMD level), this patch adds the 1GB
> page(PUD level) support.
>
> This is useful on large machines to save some reserved memory
> (as paging structures) in the kdump case when kexec setups up
> identity mappings before booting into the new kernel.
>
> We will utilize this new support in the following patch.
>
> Signed-off-by: Xunlei Pang <xlpang@xxxxxxxxxx>
> ---
>  arch/x86/boot/compressed/pagetable.c |  2 +-
>  arch/x86/include/asm/init.h          |  3 ++-
>  arch/x86/kernel/machine_kexec_64.c   |  2 +-
>  arch/x86/mm/ident_map.c              | 13 ++++++++++++-
>  arch/x86/power/hibernate_64.c        |  2 +-
>  5 files changed, 17 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/pagetable.c b/arch/x86/boot/compressed/pagetable.c
> index 56589d0..1d78f17 100644
> --- a/arch/x86/boot/compressed/pagetable.c
> +++ b/arch/x86/boot/compressed/pagetable.c
> @@ -70,7 +70,7 @@ static void *alloc_pgt_page(void *context)
>   * Due to relocation, pointers must be assigned at run time not build time.
>   */
>  static struct x86_mapping_info mapping_info = {
> -       .pmd_flag       = __PAGE_KERNEL_LARGE_EXEC,
> +       .page_flag       = __PAGE_KERNEL_LARGE_EXEC,
>  };
>
>  /* Locates and clears a region for a new top level page table. */
> diff --git a/arch/x86/include/asm/init.h b/arch/x86/include/asm/init.h
> index 737da62..46eab1a 100644
> --- a/arch/x86/include/asm/init.h
> +++ b/arch/x86/include/asm/init.h
> @@ -4,8 +4,9 @@
>  struct x86_mapping_info {
>         void *(*alloc_pgt_page)(void *); /* allocate buf for page table */
>         void *context;                   /* context for alloc_pgt_page */
> -       unsigned long pmd_flag;          /* page flag for PMD entry */
> +       unsigned long page_flag;         /* page flag for PMD or PUD entry */
>         unsigned long offset;            /* ident mapping offset */
> +       bool use_pud_page;              /* PUD level 1GB page support */

how about use direct_gbpages instead?
use_pud_page is confusing.

>  };
>
>  int kernel_ident_mapping_init(struct x86_mapping_info *info, pgd_t *pgd_page,
> diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
> index 085c3b3..1d4f2b0 100644
> --- a/arch/x86/kernel/machine_kexec_64.c
> +++ b/arch/x86/kernel/machine_kexec_64.c
> @@ -113,7 +113,7 @@ static int init_pgtable(struct kimage *image, unsigned long start_pgtable)
>         struct x86_mapping_info info = {
>                 .alloc_pgt_page = alloc_pgt_page,
>                 .context        = image,
> -               .pmd_flag       = __PAGE_KERNEL_LARGE_EXEC,
> +               .page_flag      = __PAGE_KERNEL_LARGE_EXEC,
>         };
>         unsigned long mstart, mend;
>         pgd_t *level4p;
> diff --git a/arch/x86/mm/ident_map.c b/arch/x86/mm/ident_map.c
> index 04210a2..0ad0280 100644
> --- a/arch/x86/mm/ident_map.c
> +++ b/arch/x86/mm/ident_map.c
> @@ -13,7 +13,7 @@ static void ident_pmd_init(struct x86_mapping_info *info, pmd_t *pmd_page,
>                 if (pmd_present(*pmd))
>                         continue;
>
> -               set_pmd(pmd, __pmd((addr - info->offset) | info->pmd_flag));
> +               set_pmd(pmd, __pmd((addr - info->offset) | info->page_flag));
>         }
>  }
>
> @@ -30,6 +30,17 @@ static int ident_pud_init(struct x86_mapping_info *info, pud_t *pud_page,
>                 if (next > end)
>                         next = end;
>
> +               if (info->use_pud_page) {
> +                       pud_t pudval;
> +
> +                       if (pud_present(*pud))
> +                               continue;
> +
> +                       pudval = __pud((addr - info->offset) | info->page_flag);
> +                       set_pud(pud, pudval);

should mask addr with PUD_MASK.
   addr &= PUD_MASK;
   set_pud(pud, __pmd(addr - info->offset) | info->page_flag);



> +                       continue;
> +               }
> +
>                 if (pud_present(*pud)) {
>                         pmd = pmd_offset(pud, 0);
>                         ident_pmd_init(info, pmd, addr, next);
> diff --git a/arch/x86/power/hibernate_64.c b/arch/x86/power/hibernate_64.c
> index 6a61194..a6e21fe 100644
> --- a/arch/x86/power/hibernate_64.c
> +++ b/arch/x86/power/hibernate_64.c
> @@ -104,7 +104,7 @@ static int set_up_temporary_mappings(void)
>  {
>         struct x86_mapping_info info = {
>                 .alloc_pgt_page = alloc_pgt_page,
> -               .pmd_flag       = __PAGE_KERNEL_LARGE_EXEC,
> +               .page_flag      = __PAGE_KERNEL_LARGE_EXEC,
>                 .offset         = __PAGE_OFFSET,
>         };
>         unsigned long mstart, mend;
> --
> 1.8.3.1
>