Messages in this thread | | | Date | Wed, 13 Dec 2017 15:34:55 +0100 | From | Peter Zijlstra <> | Subject | Re: [patch 05/16] mm: Allow special mappings with user access cleared |
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On Wed, Dec 13, 2017 at 03:57:40PM +0300, Kirill A. Shutemov wrote: > On Wed, Dec 13, 2017 at 01:22:11PM +0100, Peter Zijlstra wrote:
> > get_user_pages_fast() will ultimately end up doing > > pte_access_permitted() before getting the page, follow_page OTOH does > > not do this, which makes for a curious difference between the two. > > > > So I'm thinking we want the below irrespective of the VM_NOUSER patch, > > but with VM_NOUSER it would mean write(2) will no longer be able to > > access the page. > > Oh.. > > We do call pte_access_permitted(), but only for write access. > See can_follow_write_pte().
My can_follow_write_pte() looks like:
static inline bool can_follow_write_pte(pte_t pte, unsigned int flags) { return pte_write(pte) || ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte)); }
am I perchance looking at the wrong tee?
> The issue seems bigger: we also need such calls for other page table levels :-/
Sure.
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