On Fri, Jun 21, 2019 at 11:05:42AM -0300, Jason Gunthorpe wrote:

Today this check is only being done on the get_user_pages_fast() -
after this patch it is also done for __get_user_pages_fast().

Which means __get_user_pages_fast is now non-functional on a range of
MIPS CPUs, but that seems OK as far as I can tell, so:

However, looks to me like this patch is also a bug fix for this:

Yes.

quoted

-	pgdp = pgd_offset(mm, addr);
-	do {
-		pgd_t pgd = *pgdp;
-
-		next = pgd_addr_end(addr, end);
-		if (pgd_none(pgd))
-			goto slow;
-		if (!gup_pud_range(pgd, addr, next, gup_flags & FOLL_WRITE,
-				   pages, &nr))

This is different too, the core code has a p4d layer, but I see that
whole thing gets NOP'd by the compiler as mips uses pgtable-nop4d.h -
right?

Exactly.