"Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx> writes: > On 2/21/19 5:42 PM, Jan Kara wrote: >> Hi Aneesh, >> >> On Thu 21-02-19 12:52:39, Aneesh Kumar K.V wrote: >>> We found this while testing dax with XFS, but i guess this is true for >>> other file systems too. The stack trace looks as >>> > >>> I guess iomap code doesn't handle this correctly? Or am I missing >>> some other ways we can end up flushing tlb? >> >> So for RW->RO transition we use ptep_clear_flush() in dax_entry_mkclean() >> so that one is certainly safe. Similarly for unmapping. The RO->RW >> transition does not seem to have any TLB flush so there TLB could still >> carry stale information but it's the same as with normal page faults on >> invalid PTEs or with protection faults for normal pages (see e.g. >> finish_mkwrite_fault()). > > I am not sure i understood that. RO -> RW transition can have stale TLB > entries with RO mapping in them. So architecture do flush TLB during the > fault, some may not. We do have a NestMMU issue with that transition > which requires us to do mark the pte invalid and flush TLB for that > transition. (see commit bd5050e38aec3055ff4257ade987d808ac93b582 ) > > For invalid PTEs we should have a TLB entry at all. For invalid PTEs we should not have a TLB entry at all. -aneesh
