On Mon, 16 Nov 2015, Dave Hansen wrote:
> +static inline int pte_allows_gup(pte_t pte, int write)
> +{
> + /*
> + * 'entry_flags' can come from a pte, pmd or pud. Make
> + * sure to only check flags here that are valid *and* the
> + * same value on all 3 types. (PAT is currently the only
> + * one where that is true and is not checked here).
I have a hard time to understand that comment.
/*
* 'entry_flags' can come from a pte, pmd or pud. We only check
* _PAGE_PRESENT, _PAGE_USER and _PAGE_RW here, which are the
* same for all types.
*/
Is that what you wanted to say?
> + */
> + if (!(pte_flags(pte) & (_PAGE_PRESENT|_PAGE_USER)))
> + return 0;
> + if (write && !(pte_write(pte)))
> + return 0;
> + return 1;
> +}
> +
> +static inline int pmd_allows_gup(pmd_t pmd, int write)
> +{
> + return pte_allows_gup(*(pte_t *)&pmd, write);
> +}
> +
> +static inline int pud_allows_gup(pud_t pud, int write)
> +{
> + return pte_allows_gup(*(pte_t *)&pud, write);
> +}
> +
> static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr,
> unsigned long end, int write, struct page **pages, int *nr)
> {
> - unsigned long mask;
> struct page *head, *page;
> int refs;
>
> - mask = _PAGE_PRESENT|_PAGE_USER;
> - if (write)
> - mask |= _PAGE_RW;
> - if ((pmd_flags(pmd) & mask) != mask)
> + if (!pmd_allows_gup(pmd, write))
Why do you need that extra indirection here of rereading the pmd?
You have the pmd already.
Thanks,
tglx
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