On Wed, Jan 6, 2021 at 9:11 PM Willem de Bruijn <willemb@xxxxxxxxxx> wrote: > > On Wed, Jan 6, 2021 at 8:49 PM Jakub Kicinski <kuba@xxxxxxxxxx> wrote: > > > > On Wed, 6 Jan 2021 17:03:48 -0800 Linus Torvalds wrote: > > > I wonder whether there is other code that "knows" about kmap() only > > > affecting PageHighmem() pages thing that is no longer true. > > > > > > Looking at some other code, skb_gro_reset_offset() looks suspiciously > > > like it also thinks highmem pages are special. > > > > > > Adding the networking people involved in this area to the cc too. But there are three other kmap_atomic callers under net/ that do not loop at all, so assume non-compound pages. In esp_output_head, esp6_output_head and skb_seq_read. The first two directly use skb_page_frag_refill, which can allocate compound (but not __GFP_HIGHMEM) pages, and the third can be inserted with netfilter xt_string in the path of tcp transmit skbs, which can also have compound pages. I think that these could similarly access data beyond the end of the kmap_atomic mapped page. I'll take a closer look.
