Functions that work on a pointer to virtual memory such as virt_to_pfn()
and users of that function such as virt_to_page() are supposed to pass a
pointer to virtual memory, ideally a (void *) or other pointer.  However
since many architectures implement virt_to_pfn() as a macro, this function
becomes polymorphic and accepts both a (unsigned long) and a (void *).

If we instead implement a proper virt_to_pfn(void *addr) function the
following happens (occurred on arch/arm):

  mm/gup.c: In function '__get_user_pages_locked':
  mm/gup.c:1599:49: warning: passing argument 1 of 'virt_to_pfn'
    makes pointer from integer without a cast [-Wint-conversion]
    pages[i] = virt_to_page(start);

Fix this with an explicit cast.

Link: https://lkml.kernel.org/r/20220630084124.691207-5-linus.walleij@linaro.orgSigned-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Marco Elver <elver@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>