On Tue, Apr 17, 2018 at 8:03 PM, Laurent Dufour <ldufour@xxxxxxxxxxxxxxxxxx> wrote: > pte_unmap_same() is making the assumption that the page table are still > around because the mmap_sem is held. > This is no more the case when running a speculative page fault and > additional check must be made to ensure that the final page table are still > there. > > This is now done by calling pte_spinlock() to check for the VMA's > consistency while locking for the page tables. > > This is requiring passing a vm_fault structure to pte_unmap_same() which is > containing all the needed parameters. > > As pte_spinlock() may fail in the case of a speculative page fault, if the > VMA has been touched in our back, pte_unmap_same() should now return 3 > cases : > 1. pte are the same (0) > 2. pte are different (VM_FAULT_PTNOTSAME) > 3. a VMA's changes has been detected (VM_FAULT_RETRY) > > The case 2 is handled by the introduction of a new VM_FAULT flag named > VM_FAULT_PTNOTSAME which is then trapped in cow_user_page(). > If VM_FAULT_RETRY is returned, it is passed up to the callers to retry the > page fault while holding the mmap_sem. > > Acked-by: David Rientjes <rientjes@xxxxxxxxxx> > Signed-off-by: Laurent Dufour <ldufour@xxxxxxxxxxxxxxxxxx> > --- > include/linux/mm.h | 1 + > mm/memory.c | 39 ++++++++++++++++++++++++++++----------- > 2 files changed, 29 insertions(+), 11 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 4d1aff80669c..714da99d77a3 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1208,6 +1208,7 @@ static inline void clear_page_pfmemalloc(struct page *page) > #define VM_FAULT_NEEDDSYNC 0x2000 /* ->fault did not modify page tables > * and needs fsync() to complete (for > * synchronous page faults in DAX) */ > +#define VM_FAULT_PTNOTSAME 0x4000 /* Page table entries have changed */ This has to be added to VM_FAULT_RESULT_TRACE ?
