[PATCH v3 1/5] mm/sparse-vmemmap: provide generic vmemmap_set_pmd() and vmemmap_check_pmd()

[Muchun Song]

The two weak functions are currently no-ops on every architecture,
forcing each platform that needs them to duplicate the same handful
of lines.  Provide a generic implementation:

- vmemmap_set_pmd() simply sets a huge PMD with PAGE_KERNEL protection.

- vmemmap_check_pmd() verifies that the PMD is present and leaf,
  then calls the existing vmemmap_verify() helper.

Architectures that need special handling can continue to override the
weak symbols; everyone else gets the standard version for free.

Signed-off-by: Muchun Song <songmuchun at bytedance.com>
---
v2->v3:
- Replace BUG_ON() with WARN_ON_ONCE() in vmemmap_set_pmd()
---
 mm/sparse-vmemmap.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index 112ccf9c71ca..99e2be39671b 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -386,12 +386,17 @@ int __meminit vmemmap_populate_hvo(unsigned long addr, unsigned long end,
 void __weak __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node,
 				      unsigned long addr, unsigned long next)
 {
+	WARN_ON_ONCE(!pmd_set_huge(pmd, virt_to_phys(p), PAGE_KERNEL));
 }
 
 int __weak __meminit vmemmap_check_pmd(pmd_t *pmd, int node,
 				       unsigned long addr, unsigned long next)
 {
-	return 0;
+	if (!pmd_leaf(pmdp_get(pmd)))
+		return 0;
+	vmemmap_verify((pte_t *)pmd, node, addr, next);
+
+	return 1;
 }
 
 int __meminit vmemmap_populate_hugepages(unsigned long start, unsigned long end,
-- 
2.54.0