From: Willem de Bruijn <willemdebruijn.ker...@gmail.com> Date: Thu, 22 Jun 2017 16:57:07 -0400
>> >> Likewise. >> >>> + f_off = f->page_offset; >>> + f_size = f->size; >>> + >>> + vaddr = kmap_atomic(skb_frag_page(f)); >> >> I looked at some kmap_atomic() implementations and I do not think >> it supports compound pages. > > Indeed. Thanks. It appears that I can do the obvious thing and > kmap the individual page that is being copied inside the loop: > > kmap_atomic(skb_frag_page(f) + (f_off >> PAGE_SHIFT)); > > This is similar to existing logic in copy_huge_page_from_user > and __flush_dcache_page in arch/arm/mm/flush.c > > But, this also applies to other skb operations that call kmap_atomic, > such as skb_copy_bits and __skb_checksum. Not all can be called > from a codepath with a compound user page, but I have to address > the ones that can. Yeah that's quite a mess, it looks like this assumption that kmap can handle compound pages exists in quite a few places.
