Messages in this thread Patch in this message | | | Date | Thu, 3 Feb 2011 17:56:57 +0000 | From | Russell King - ARM Linux <> | Subject | Re: [PATCH v4 09/19] ARM: LPAE: Page table maintenance for the 3-level format |
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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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