mm/arch: provide pud_pfn() fallback

The comment in the code explains the reasons.  We took a different
approach comparing to pmd_pfn() by providing a fallback function.

Another option is to provide some lower level config options (compare to
HUGETLB_PAGE or THP) to identify which layer an arch can support for such
huge mappings.  However that can be an overkill.

[[email protected]: fix loongson defconfig]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Peter Xu <[email protected]>
Reviewed-by: Jason Gunthorpe <[email protected]>
Tested-by: Ryan Roberts <[email protected]>
Cc: Mike Rapoport (IBM) <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Andrew Jones <[email protected]>
Cc: Aneesh Kumar K.V (IBM) <[email protected]>
Cc: Axel Rasmussen <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: James Houghton <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Yang Shi <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 14 insertions, 0 deletions

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 09c85c7bf9c2..f108c7a3c1d9 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1820,6 +1820,20 @@ typedef unsigned int pgtbl_mod_mask;
 #endif
 
 /*
+ * We always define pmd_pfn for all archs as it's used in lots of generic
+ * code.  Now it happens too for pud_pfn (and can happen for larger
+ * mappings too in the future; we're not there yet).  Instead of defining
+ * it for all archs (like pmd_pfn), provide a fallback.
+ *
+ * Note that returning 0 here means any arch that didn't define this can
+ * get severely wrong when it hits a real pud leaf.  It's arch's
+ * responsibility to properly define it when a huge pud is possible.
+ */
+#ifndef pud_pfn
+#define pud_pfn(x) 0
+#endif
+
+/*
  * Some architectures have MMUs that are configurable or selectable at boot
  * time. These lead to variable PTRS_PER_x. For statically allocated arrays it
  * helps to have a static maximum value.