Re: [PATCH 1/2] arm64: Get existing page protections in split_pmd

Xishi Qiu
2015-11-05T10:18:37Z

On 2015/11/4 5:48, Laura Abbott wrote:

>
> Rather than always putting the least restrictived permissions
> (PAGE_KERNEL_EXEC) when spliting a pmd into pages, use
> the existing permissions from the pmd for the page.
>
> Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
> ---
> arch/arm64/mm/mmu.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 9211b85..ff41efa 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -75,14 +75,13 @@ static void __init *early_alloc(unsigned long sz)
> static void split_pmd(pmd_t *pmd, pte_t *pte)
> {
> unsigned long pfn = pmd_pfn(*pmd);
> + unsigned long addr = pfn << PAGE_SHIFT;
> + pgprot_t prot = __pgprot(pmd_val(*pmd) ^ addr) | PTE_TYPE_PAGE;
> +

Hi Laura,

I'm not quite understand, I find split_pud() doesn't set the flag
PMD_TYPE_TABLE. If we clear xx_TABLE_BIT, does that means the page
is large page?
And what is the different from the flag xx_TYPE_SECT?

Thanks,
Xishi Qiu

> int i = 0;
>
> do {
> - /*
> - * Need to have the least restrictive permissions available
> - * permissions will be fixed up later
> - */
> - set_pte(pte, pfn_pte(pfn, PAGE_KERNEL_EXEC));
> + set_pte(pte, pfn_pte(pfn, prot));

> pfn++;
> } while (pte++, i++, i < PTRS_PER_PTE);
> }