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SubjectRe: [RFC] ARC: mm: Restrict definition of pfn_valid() macro for CONFIG_FLATMEM
On Tue 29-11-16 18:29:06, Yuriy Kolerov wrote:
> Despite the fact that subtraction of unsigned integers is a defined
> behaviour however such operations can lead to unexpected results. Thus
> it is better to check both left and right boundaries to avoid potential
> bugs as it done in the generic page.h.

Why and which code would use an out of range pfn? Why other arches do
not need to care?

>
> Signed-off-by: Yuriy Kolerov <yuriy.kolerov@synopsys.com>
> ---
> arch/arc/include/asm/page.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arc/include/asm/page.h b/arch/arc/include/asm/page.h
> index 296c342..81cfc6c7 100644
> --- a/arch/arc/include/asm/page.h
> +++ b/arch/arc/include/asm/page.h
> @@ -88,7 +88,7 @@ typedef pte_t * pgtable_t;
> #define ARCH_PFN_OFFSET virt_to_pfn(CONFIG_LINUX_LINK_BASE)
>
> #ifdef CONFIG_FLATMEM
> -#define pfn_valid(pfn) (((pfn) - ARCH_PFN_OFFSET) < max_mapnr)
> +#define pfn_valid(pfn) ((pfn) >= ARCH_PFN_OFFSET && ((pfn) - ARCH_PFN_OFFSET) < max_mapnr)
> #endif
>
> /*
> --
> 2.7.4
>

--
Michal Hocko
SUSE Labs

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