Currently DAX folio/page reference counts are managed differently to
normal pages. To allow these to be managed the same as normal pages
introduce vmf_insert_folio_pmd. This will map the entire PMD-sized folio
and take references as it would for a normally mapped page.

This is distinct from the current mechanism, vmf_insert_pfn_pmd, which
simply inserts a special devmap PMD entry into the page table without
holding a reference to the page for the mapping.

Signed-off-by: Alistair Popple <apopple@nvidia.com>

---

Changes for v5:
 - Minor code cleanup suggested by David
---
 include/linux/huge_mm.h |  1 +-
 mm/huge_memory.c        | 54 ++++++++++++++++++++++++++++++++++--------
 2 files changed, 45 insertions(+), 10 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 5bd1ff7..3633bd3 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h

@@ -39,6 +39,7 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 
 vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, pfn_t pfn, bool write);
 vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write);
+vm_fault_t vmf_insert_folio_pmd(struct vm_fault *vmf, struct folio *folio, bool write);
 vm_fault_t vmf_insert_folio_pud(struct vm_fault *vmf, struct folio *folio, bool write);
 
 enum transparent_hugepage_flag {

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 256adc3..d1ea76e 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c

@@ -1381,14 +1381,12 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
 {
 	struct mm_struct *mm = vma->vm_mm;
 	pmd_t entry;
-	spinlock_t *ptl;
 
-	ptl = pmd_lock(mm, pmd);