[PATCH] arm64: Don't report clear pmds and puds as huge

[Catalin Marinas]

On Wed, Jul 01, 2015 at 02:08:31PM +0200, Christoffer Dall wrote:
> The current pmd_huge() and pud_huge() functions simply check if the table
> bit is not set and reports the entries as huge in that case.  This is
> counter-intuitive as a clear pmd/pud cannot also be a huge pmd/pud, and
> it is inconsistent with at least arm and x86.
> 
> To prevent others from making the same mistake as me in looking at code
> that calls these functions and to fix an issue with KVM on arm64 that
> causes memory corruption due to incorrect page reference counting
> resulting from this mistake, let's change the behavior.
> 
> Cc: stable at vger.kernel.org
> Signed-off-by: Christoffer Dall <christoffer.dall at linaro.org>
> ---
>  arch/arm64/mm/hugetlbpage.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
> index 2de9d2e..0eeb4f09 100644
> --- a/arch/arm64/mm/hugetlbpage.c
> +++ b/arch/arm64/mm/hugetlbpage.c
> @@ -40,13 +40,13 @@ int huge_pmd_unshare(struct mm_struct *mm, unsigned long *addr, pte_t *ptep)
>  
>  int pmd_huge(pmd_t pmd)
>  {
> -	return !(pmd_val(pmd) & PMD_TABLE_BIT);
> +	return pmd_val(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT);
>  }
>  
>  int pud_huge(pud_t pud)
>  {
>  #ifndef __PAGETABLE_PMD_FOLDED
> -	return !(pud_val(pud) & PUD_TABLE_BIT);
> +	return pud_val(pud) && !(pud_val(pud) & PUD_TABLE_BIT);
>  #else
>  	return 0;
>  #endif

Thanks for the patch, I'll add the acks/reviews and Fixes: tags.

(and I think I'll change pmd_val to pmd_present, same for pud; no
functional difference)

-- 
Catalin