On Thu, Apr 04, 2019 at 09:50:47AM -0700, Ira Weiny wrote: > On Thu, Apr 04, 2019 at 03:23:47PM +0800, Huang Shijie wrote: > > When CONFIG_HAVE_GENERIC_GUP is defined, the kernel will use its own > > get_user_pages_fast(). > > > > In the following scenario, we will may meet the bug in the DMA case: > > ..................... > > get_user_pages_fast(start,,, pages); > > ...... > > sg_alloc_table_from_pages(, pages, ...); > > ..................... > > > > The root cause is that sg_alloc_table_from_pages() requires the > > page order to keep the same as it used in the user space, but > > get_user_pages_fast() will mess it up. > > I wonder if there is something we can do to change sg_alloc_table_from_pages() > to work? Reading the comment for it there is no indication of this limitation. The sg_alloc_table_from_pages() cannot work if the page order is wrong... > So should we update that comment as well? Okay. I will create a DMA patch to add more comment for sg_alloc_table_from_pages(). Thanks Huang Shijie
