mm/hmm: only define hmm_vma_walk_pud if needed

We only need the special pud_entry walker if PUD-sized hugepages and pte
mappings are supported, else the common pagewalk code will take care of
the iteration.  Not implementing this callback reduced the amount of code
compiled for non-x86 platforms, and also fixes compile failures with other
architectures when helpers like pud_pfn are not implemented.

Link: https://lore.kernel.org/r/20190806160554.14046-11-hch@lst.deSigned-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

mm/hmm.c

@@ -456,15 +456,6 @@ static inline uint64_t pmd_to_hmm_pfn_flags(struct hmm_range *range, pmd_t pmd)
 				range->flags[HMM_PFN_VALID];
 }
 
-static inline uint64_t pud_to_hmm_pfn_flags(struct hmm_range *range, pud_t pud)
-{
-	if (!pud_present(pud))
-		return 0;
-	return pud_write(pud) ? range->flags[HMM_PFN_VALID] |
-				range->flags[HMM_PFN_WRITE] :
-				range->flags[HMM_PFN_VALID];
-}
-
 static int hmm_vma_handle_pmd(struct mm_walk *walk,
 			      unsigned long addr,
 			      unsigned long end,
@@ -705,9 +696,18 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp,
 	return 0;
 }
 
-static int hmm_vma_walk_pud(pud_t *pudp,
-			    unsigned long start,
-			    unsigned long end,
+#if defined(CONFIG_ARCH_HAS_PTE_DEVMAP) && \
+    defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
+static inline uint64_t pud_to_hmm_pfn_flags(struct hmm_range *range, pud_t pud)
+{
+	if (!pud_present(pud))
+		return 0;
+	return pud_write(pud) ? range->flags[HMM_PFN_VALID] |
+				range->flags[HMM_PFN_WRITE] :
+				range->flags[HMM_PFN_VALID];
+}
+
+static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
 		struct mm_walk *walk)
 {
 	struct hmm_vma_walk *hmm_vma_walk = walk->private;
@@ -772,6 +772,9 @@ static int hmm_vma_walk_pud(pud_t *pudp,
 
 	return 0;
 }
+#else
+#define hmm_vma_walk_pud	NULL
+#endif
 
 static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask,
 				      unsigned long start, unsigned long end,