On Thu, Jul 14, 2016 at 09:04:18PM -0400, Rik van Riel wrote: > On Fri, 2016-07-15 at 09:20 +1000, Balbir Singh wrote: > > > > == > > > + ((unsigned long)end & (unsigned > > > long)PAGE_MASK))) > > > + return NULL; > > > + > > > + /* Allow if start and end are inside the same compound > > > page. */ > > > + endpage = virt_to_head_page(end); > > > + if (likely(endpage == page)) > > > + return NULL; > > > + > > > + /* Allow special areas, device memory, and sometimes > > > kernel data. */ > > > + if (PageReserved(page) && PageReserved(endpage)) > > > + return NULL; > > > > If we came here, it's likely that endpage > page, do we need to check > > that only the first and last pages are reserved? What about the ones > > in > > the middle? > > I think this will be so rare, we can get away with just > checking the beginning and the end. > But do we want to leave a hole where an aware user space can try a longer copy_* to avoid this check? If it is unlikely should we just bite the bullet and do the check for the entire range? Balbir Singh. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>