Thomas Hellström wrote: >Benjamin Herrenschmidt wrote: > > > > >Hmm, the comments to handle_pte_fault(), which is calling do_nopage >gives some insight.. > > * Note the "page_table_lock". It is to protect against kswapd removing > * pages from under us. Note that kswapd only ever _removes_ pages, never > * adds them. As such, once we have noticed that the page is not present, > * we can drop the lock early. > * > * The adding of pages is protected by the MM semaphore (which we hold), > * so we don't need to worry about a page being suddenly been added into > * our VM. > * > >So basically when driver nopage is called we should _never_ have a valid >PTE. > > ...Or perhaps that comment is a remnant from the time when the mm semaphore wasn't a rw semaphore.
/Thomas >This makes the extra check in do_nopage() after the call to driver >nopage() somewhat mysterious, (but fortunate). Perhaps the intention is >for driver nopage() to be able to temporarily release the MM semaphore. >(Which would be even more fortunate). > >In any case, if the comments hold, we should never hit the BUG() >statement in io_remap_pfn_range(), but it also seems clear that the code >doesn't really expect ptes to be added. > >Taking this to the lkml for some clarification might be a good idea. > >On a totally different subject, the previous discussion we had about >having pages outside of the kernel virtual map (highmem pages) for >example, might be somewhat tricky with the current definition of >alloc_gatt_pages and free_gatt_pages, which both returns kernel virtual >addresses. Would be nice to have them return struct page* instead. > > >/Thomas > > > > > > >------------------------------------------------------------------------- >Take Surveys. Earn Cash. Influence the Future of IT >Join SourceForge.net's Techsay panel and you'll get the chance to share your >opinions on IT & business topics through brief surveys -- and earn cash >http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV >-- >_______________________________________________ >Dri-devel mailing list >Dri-devel@lists.sourceforge.net >https://lists.sourceforge.net/lists/listinfo/dri-devel > > ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys -- and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV -- _______________________________________________ Dri-devel mailing list Dri-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/dri-devel
