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SubjectRe: [PATCH v4 09/19] ARM: LPAE: Page table maintenance for the 3-level format
On Mon, Jan 24, 2011 at 05:55:51PM +0000, Catalin Marinas wrote:
> The patch also introduces the L_PGD_SWAPPER flag to mark pgd entries
> pointing to pmd tables pre-allocated in the swapper_pg_dir and avoid
> trying to free them at run-time. This flag is 0 with the classic page
> table format.
This shouldn't be necessary.

> diff --git a/arch/arm/mm/pgd.c b/arch/arm/mm/pgd.c
> index 709244c..003587d 100644
> --- a/arch/arm/mm/pgd.c
> +++ b/arch/arm/mm/pgd.c
> @@ -10,6 +10,7 @@
> #include <linux/mm.h>
> #include <linux/gfp.h>
> #include <linux/highmem.h>
> +#include <linux/slab.h>
>
> #include <asm/pgalloc.h>
> #include <asm/page.h>
> @@ -17,6 +18,14 @@
>
> #include "mm.h"
>
> +#ifdef CONFIG_ARM_LPAE
> +#define __pgd_alloc() kmalloc(PTRS_PER_PGD * sizeof(pgd_t), GFP_KERNEL)
> +#define __pgd_free(pgd) kfree(pgd)
> +#else
> +#define __pgd_alloc() (pgd_t *)__get_free_pages(GFP_KERNEL, 2)
> +#define __pgd_free(pgd) free_pages((unsigned long)pgd, 2)
> +#endif
> +
> /*
> * need to get a 16k page for level 1
> */
> @@ -26,7 +35,7 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
> pmd_t *new_pmd, *init_pmd;
> pte_t *new_pte, *init_pte;
>
> - new_pgd = (pgd_t *)__get_free_pages(GFP_KERNEL, 2);
> + new_pgd = __pgd_alloc();
> if (!new_pgd)
> goto no_pgd;
>
> @@ -41,12 +50,21 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
>
> clean_dcache_area(new_pgd, PTRS_PER_PGD * sizeof(pgd_t));
>
> +#ifdef CONFIG_ARM_LPAE
> + /*
> + * Allocate PMD table for modules and pkmap mappings.
> + */
> + new_pmd = pmd_alloc(mm, new_pgd + pgd_index(MODULES_VADDR), 0);
> + if (!new_pmd)
> + goto no_pmd;

This should be a copy of the same page tables found in swapper_pg_dir -
that's what the memcpy() above is doing.

> +#endif
> +
> if (!vectors_high()) {
> /*
> * On ARM, first page must always be allocated since it
> * contains the machine vectors.
> */
> - new_pmd = pmd_alloc(mm, new_pgd, 0);
> + new_pmd = pmd_alloc(mm, new_pgd + pgd_index(0), 0);

However, the first pmd table, and the first pte table only need to be
present for the reason stated in the comment, and these need to be
allocated.

> if (!new_pmd)
> goto no_pmd;
>
> @@ -66,7 +84,7 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
> no_pte:
> pmd_free(mm, new_pmd);
> no_pmd:
> - free_pages((unsigned long)new_pgd, 2);
> + __pgd_free(new_pgd);
> no_pgd:
> return NULL;
> }
> @@ -80,20 +98,36 @@ void pgd_free(struct mm_struct *mm, pgd_t *pgd_base)
> if (!pgd_base)
> return;
>
> - pgd = pgd_base + pgd_index(0);
> - if (pgd_none_or_clear_bad(pgd))
> - goto no_pgd;
> + if (!vectors_high()) {

No, that's wrong. As FIRST_USER_ADDRESS is nonzero, the first pmd and
pte table will remain allocated in spite of free_pgtables(), so this
results in a memory leak.

> + pgd = pgd_base + pgd_index(0);
> + if (pgd_none_or_clear_bad(pgd))
> + goto no_pgd;
>
> - pmd = pmd_offset(pgd, 0);
> - if (pmd_none_or_clear_bad(pmd))
> - goto no_pmd;
> + pmd = pmd_offset(pgd, 0);
> + if (pmd_none_or_clear_bad(pmd))
> + goto no_pmd;
>
> - pte = pmd_pgtable(*pmd);
> - pmd_clear(pmd);
> - pte_free(mm, pte);
> + pte = pmd_pgtable(*pmd);
> + pmd_clear(pmd);
> + pte_free(mm, pte);
> no_pmd:
> - pgd_clear(pgd);
> - pmd_free(mm, pmd);
> + pgd_clear(pgd);
> + pmd_free(mm, pmd);
> + }
> no_pgd:
> - free_pages((unsigned long) pgd_base, 2);
> +#ifdef CONFIG_ARM_LPAE
> + /*
> + * Free modules/pkmap or identity pmd tables.
> + */
> + for (pgd = pgd_base; pgd < pgd_base + PTRS_PER_PGD; pgd++) {
> + if (pgd_none_or_clear_bad(pgd))
> + continue;
> + if (pgd_val(*pgd) & L_PGD_SWAPPER)
> + continue;
> + pmd = pmd_offset(pgd, 0);
> + pgd_clear(pgd);
> + pmd_free(mm, pmd);
> + }
> +#endif

And as kernel mappings in the pgd above TASK_SIZE are supposed to be
identical across all page tables, this shouldn't be necessary.


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