On Fri, Nov 16, 2012 at 07:39:11PM -0800, Yinghai Lu wrote:
> During test patch that adjust page_size_mask to map small range ram with
> big page size, found page table is setup wrongly for 32bit. And
Which patch is that? x86, mm: Add global page_size_mask and probe one time only
Can you include the name here please.
> native_pagetable_init wrong clear pte for pmd with large page support.
^^^^^-> wrongly cleared
>
> 1. add more comments about why we are expecting pte.
>
> 2. add BUG checking, so next time we could find problem earlier
> when we mess up page table setup again.
Not very optimistic about future changes, eh?
>
> 3. max_low_pfn is not included boundary for low memory mapping.
> We should check from max_low_pfn instead of +1.
>
> 4. add print out when some pte really get cleared, or we should use
> WARN() to find out why above max_low_pfn get mapped? so we could
> fix it.
I would think WARN? Easier to spot and get bug emails.
>
> Signed-off-by: Yinghai Lu <ying...@kernel.org>
> ---
> arch/x86/mm/init_32.c | 18 ++++++++++++++++--
> 1 files changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
> index 322ee56..19ef9f0 100644
> --- a/arch/x86/mm/init_32.c
> +++ b/arch/x86/mm/init_32.c
> @@ -480,9 +480,14 @@ void __init native_pagetable_init(void)
>
> /*
> * Remove any mappings which extend past the end of physical
> - * memory from the boot time page table:
> + * memory from the boot time page table.
> + * In virtual address space, we should have at least two pages
> + * from VMALLOC_END to pkmap or fixmap according to VMALLOC_END
> + * definition. And max_low_pfn is set to VMALLOC_END physical
> + * address. If initial memory mapping is doing right job, we
> + * should have pte used near max_low_pfn or one pmd is not present.
'have pte used near' ?
Do you mean we should have an used PTE near max_low_pfn and one
empty PMD?
> */
> - for (pfn = max_low_pfn + 1; pfn < 1<<(32-PAGE_SHIFT); pfn++) {
> + for (pfn = max_low_pfn; pfn < 1<<(32-PAGE_SHIFT); pfn++) {
> va = PAGE_OFFSET + (pfn<<PAGE_SHIFT);
> pgd = base + pgd_index(va);
> if (!pgd_present(*pgd))
> @@ -493,10 +498,19 @@ void __init native_pagetable_init(void)
> if (!pmd_present(*pmd))
> break;
>
> + /* should not be large page here */
> + if (pmd_large(*pmd)) {
> + pr_warn("try to clear pte for ram above max_low_pfn:
> pfn: %lx pmd: %p pmd phys: %lx, but pmd is big page and is not using pte !\n",
> + pfn, pmd, __pa(pmd));
> + BUG_ON(1);
> + }
> +
> pte = pte_offset_kernel(pmd, va);
> if (!pte_present(*pte))
> break;
>
> + printk(KERN_DEBUG "clearing pte for ram above max_low_pfn: pfn:
> %lx pmd: %p pmd phys: %lx pte: %p pte phys: %lx\n",
> + pfn, pmd, __pa(pmd), pte, __pa(pte));
> pte_clear(NULL, va, pte);
> }
> paravirt_alloc_pmd(&init_mm, __pa(base) >> PAGE_SHIFT);
> --
> 1.7.7
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
