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SubjectRe: [PATCH] Fix generic hugetlb pte check return type.
On Wed, 2 Oct 2013, David Miller wrote:

> The include/asm-generic/hugetlb.h stubs that just vector huge_pte_*()
> calls to the pte_*() implementations won't work in certain situations.
>
> x86 and sparc, for example, return "unsigned long" from the bit
> checks, and just go "return pte_val(pte) & PTE_BIT_FOO;"
>

x86 should be safe since it's known that both _PAGE_BIT_RW and
_PAGE_BIT_DIRTY are <= 32.

> But since huge_pte_*() returns 'int', if any high bits on 64-bit are
> relevant, they get chopped off.
>
> The net effect is that we can loop forever trying to COW a huge page,
> because the huge_pte_write() check signals false all the time.
>
> Reported-by: Gurudas Pai <gurudas.pai@oracle.com>
> Signed-off-by: David S. Miller <davem@davemloft.net>

Acked-by: David Rientjes <rientjes@google.com>

> ---
>
> Anyone mind if I push this through the sparc tree?
>

Makes sense since it's the only arch that appears affected.

> diff --git a/include/asm-generic/hugetlb.h b/include/asm-generic/hugetlb.h
> index d06079c..99b490b 100644
> --- a/include/asm-generic/hugetlb.h
> +++ b/include/asm-generic/hugetlb.h
> @@ -6,12 +6,12 @@ static inline pte_t mk_huge_pte(struct page *page, pgprot_t pgprot)
> return mk_pte(page, pgprot);
> }
>
> -static inline int huge_pte_write(pte_t pte)
> +static inline unsigned long huge_pte_write(pte_t pte)
> {
> return pte_write(pte);
> }
>
> -static inline int huge_pte_dirty(pte_t pte)
> +static inline unsigned long huge_pte_dirty(pte_t pte)
> {
> return pte_dirty(pte);
> }


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