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

From: Yinghai Lu
Date: Tue Apr 25 2017 - 15:50:03 EST


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
>