On Mon, Jan 13, 2025 at 05:08:31PM -0800, Dan Williams wrote:

Alistair Popple wrote:

quoted

In preparation for using insert_page() for DAX, enhance
insert_page_into_pte_locked() to handle establishing writable
mappings.  Recall that DAX returns VM_FAULT_NOPAGE after installing a
PTE which bypasses the typical set_pte_range() in finish_fault.

Signed-off-by: Alistair Popple <apopple@nvidia.com>
Suggested-by: Dan Williams <redacted>

---

Changes for v5:
 - Minor comment/formatting fixes suggested by David Hildenbrand

Changes since v2:

 - New patch split out from "mm/memory: Add dax_insert_pfn"
---
 mm/memory.c | 37 +++++++++++++++++++++++++++++--------
 1 file changed, 29 insertions(+), 8 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 06bb29e..8531acb 100644
--- a/mm/memory.c
+++ b/mm/memory.c

@@ -2126,19 +2126,40 @@ static int validate_page_before_insert(struct vm_area_struct *vma,
 }
 
 static int insert_page_into_pte_locked(struct vm_area_struct *vma, pte_t *pte,
-			unsigned long addr, struct page *page, pgprot_t prot)
+				unsigned long addr, struct page *page,
+				pgprot_t prot, bool mkwrite)
 {
 	struct folio *folio = page_folio(page);
+	pte_t entry = ptep_get(pte);
 	pte_t pteval;
 
-	if (!pte_none(ptep_get(pte)))
-		return -EBUSY;
+	if (!pte_none(entry)) {
+		if (!mkwrite)
+			return -EBUSY;
+
+		/* see insert_pfn(). */
+		if (pte_pfn(entry) != page_to_pfn(page)) {
+			WARN_ON_ONCE(!is_zero_pfn(pte_pfn(entry)));
+			return -EFAULT;
+		}
+		entry = maybe_mkwrite(entry, vma);
+		entry = pte_mkyoung(entry);
+		if (ptep_set_access_flags(vma, addr, pte, entry, 1))
+			update_mmu_cache(vma, addr, pte);
+		return 0;
+	}

This hunk feels like it is begging to be unified with insert_pfn() after
pfn_t dies. Perhaps a TODO to remember to come back and unify them, or
you can go append that work to your pfn_t removal series?

No one has complained about removing pfn_t so I do intend to clean that series
up once this has all been merged somewhere, so I will just go append this
work there.

Other than that you can add:

Reviewed-by: Dan Williams <redacted>