mm: re-allow pinning of zero pfns (again)

The below referenced commit makes the same error as 1c563432588d ("mm: fix
is_pinnable_page against a cma page"), re-interpreting the logic to
exclude pinning of the zero page, which breaks device assignment with
vfio.

To avoid further subtle mistakes, split the logic into discrete tests.

[[email protected]: simplify comment, per John]
Link: https://lkml.kernel.org/r/166015037385.760108.16881097713975517242.stgit@omen
Link: https://lore.kernel.org/all/165490039431.944052.12458624139225785964.stgit@omen
Fixes: f25cbb7a95a2 ("mm: add zone device coherent type memory support")
Signed-off-by: Alex Williamson <[email protected]>
Suggested-by: Matthew Wilcox <[email protected]>
Suggested-by: Felix Kuehling <[email protected]>
Tested-by: Slawomir Laba <[email protected]>
Reviewed-by: John Hubbard <[email protected]>
Cc: Alex Sierra <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Alistair Popple <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions