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

[Xunlei Pang]

On 04/26/2017 at 03:49 AM, Yinghai Lu wrote:
> 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.

ok

>
>>  };
>>
>>  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);

Yes, will update, thanks for the catch.

Regards,
Xunlei

>
>
>> +                       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
>>