On 4/30/06, Dave McCracken <[email protected]> wrote:
--On Friday, April 28, 2006 10:27:21 +0200 Andi Kleen <[email protected]> wrote:
>> Take a look a little further down the page for the comment.
>>
>> In i386 + PAE, pud is always present.
>
> I think his problem is that the PGD is always present too (in
> pgtables-nopud.h) Indeed looks strange.
The PGD is always fully populated on i386 if PAE is enabled. All three of
the pmd pages are allocated at page table creation time and persist till
the page table is deleted.
The following code snippet is from some kexec patch of mine. The
function is used to build a new set of page tables which are used when
jumping to the new kernel.
The code should be pretty archtecture independent - the same code
works on x86 and x86_64. And x86/PAE with a workaround.
#ifdef CONFIG_X86_PAE
#undef pud_present
#define pud_present(pud) (pud_val(pud) & _PAGE_PRESENT)
#endif
#define pa_page(page) __pa(page_address(page))
static int create_mapping(struct page *root, struct page **pages,
unsigned long va, unsigned long pa)
{
pgd_t *pgd;
pud_t *pud;
pmd_t *pmd;
pte_t *pte;
int k = 0;
pgd = (pgd_t *)page_address(root) + pgd_index(va);
if (!pgd_present(*pgd))
set_pgd(pgd, __pgd(pa_page(pages[k++]) | _KERNPG_TABLE));
pud = pud_offset(pgd, va);
if (!pud_present(*pud))
set_pud(pud, __pud(pa_page(pages[k++]) | _KERNPG_TABLE));
pmd = pmd_offset(pud, va);
if (!pmd_present(*pmd))
set_pmd(pmd, __pmd(pa_page(pages[k++]) | _KERNPG_TABLE));
pte = (pte_t *)page_address(pmd_page(*pmd)) + pte_index(va);
set_pte(pte, __pte(pa | _PAGE_KERNEL_EXEC));
return k;
}
Any comments?
/ magnus
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