On Thu 26-09-19 20:26:46, John Hubbard wrote: > On 9/26/19 3:20 AM, Kirill A. Shutemov wrote: > > BTW, have you looked at other levels of page table hierarchy. Do we have > > the same issue for PMD/PUD/... pages? > > > > Along the lines of "what other memory barriers might be missing for > get_user_pages_fast(), I'm also concerned that the synchronization between > get_user_pages_fast() and freeing the page tables might be technically broken, > due to missing memory barriers on the get_user_pages_fast() side. Details: > > gup_fast() disables interrupts, but I think it also needs some sort of > memory barrier(s), in order to prevent reads of the page table (gup_pgd_range, > etc) from speculatively happening before the interrupts are disabled. Could you be more specific about the race scenario please? I thought that the unmap path will be serialized by the pte lock. -- Michal Hocko SUSE Labs
