On Thu, Feb 2, 2017 at 11:29 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
>
> get_user_pages() relies upon find_extend_vma() to reject kernel
> addresses; the fast side of get_user_pages_fast() doesn't have anything
> of that sort
It is *supposed* to have it.
See pte_allows_gup(), for example. In particular, it requires the
_PAGE_USER bit in the PTE (and the devpte case should require
_PAGE_BIT_DEVMAP).
So no, get_user_pages_fast() can not look up kernel pages. If it does,
that would be a bug.
Linus
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