Re: [RFC][PATCH] allow bigger PAGE_OFFSET with PAE

From: William Lee Irwin III (wli@holomorphy.com)
Date: Wed Jan 08 2003 - 17:44:45 EST


On Tue, Jan 07, 2003 at 12:06:38PM -0800, Dave Hansen wrote:
>>>> Also, this gets the kernel's pagetables right, but neglects
>>>> userspace's for now. pgd_alloc() needs to be fixed to allocate
>>>> another PMD, if the split isn't PMD-alighed.

William Lee Irwin III wrote:
>>> Um, that should be automatic when USER_PTRS_PER_PGD is increased.

On Wed, Jan 08, 2003 at 01:04:23PM -0800, Dave Hansen wrote:
>> Nope, you need a little bit more. pgd_alloc() relies on its memcpy()
>> to provide the kernel mappings. After the last user PMD is allocated,
>> you still need to copy the kernel-shared part of it in.

On Wed, Jan 08, 2003 at 02:05:33PM -0800, William Lee Irwin III wrote:
> See the bit about rounding up. Then again, the pmd entries don't get
> filled in by any of that...

Okay, basically:

#define __USER_PTRS_PER_PGD (TASK_SIZE/PGDIR_SIZE)
#define PARTIAL_PGD (TASK_SIZE > __USER_PTRS_PER_PGD*PGDIR_SIZE ? 1 : 0)
#define PARTIAL_PMD ((TASK_SIZE % PGDIR_SIZE)/PMD_SIZE)
#define USER_PTRS_PER_PGD (PARTIAL_PGD + __USER_PTRS_PER_PGD)

then

pgd_t *pgd_alloc(struct mm_struct *mm)
{
        int i;
        pgd_t *pgd = kmem_cache_alloc(pae_pgd_cachep, GFP_KERNEL);

        if (pgd) {
                for (i = 0; i < USER_PTRS_PER_PGD; i++) {
                        unsigned long pmd = __get_free_page(GFP_KERNEL);
                        if (!pmd)
                                goto out_oom;
                        clear_page(pmd);
                        set_pgd(pgd + i, __pgd(1 + __pa(pmd)));
                }

                if (USER_PTRS_PER_PGD < PTRS_PER_PGD)
                        memcpy(pgd + USER_PTRS_PER_PGD,
                                swapper_pg_dir + USER_PTRS_PER_PGD,
                                (PTRS_PER_PGD-USER_PTRS_PER_PGD)*sizeof(pgd_t));

                if (PARTIAL_PGD) {
                        pgd_t *kpgd, *upgd;
                        pmd_t *kpmd, *upmd;

                        kpgd = pgd_offset_k(TASK_SIZE);
                        upgd = pgd_offset(mm, TASK_SIZE);
                        kpmd = pmd_offset(kpgd, TASK_SIZE);
                        upmd = pmd_offset(upgd, TASK_SIZE);

                        memcpy(upmd, kpmd, (PTRS_PER_PMD-PARTIAL_PMD)*sizeof(pmd_t));

                }
        }
        return pgd;
out_oom:
        for (i--; i >= 0; i--)
                free_page((unsigned long)__va(pgd_val(pgd[i])-1));
        kmem_cache_free(pae_pgd_cachep, pgd);
        return NULL;
}

etc.
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