Re: [PATCH net-next v3 02/13] sock: skb_copy_ubufs support for compound pages

Likewise.

quoted

+             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.