[PATCH v5 12/25] mm/memory: Enhance insert_page_into_pte_locked() to create writable mappings

[Alistair Popple]

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 <apop...@nvidia.com>
Suggested-by: Dan Williams <dan.j.willi...@intel.com>

---

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;
+       }
+
        /* Ok, finally just insert the thing.. */
        pteval = mk_pte(page, prot);
        if (unlikely(is_zero_folio(folio))) {
                pteval = pte_mkspecial(pteval);
        } else {
                folio_get(folio);
+               entry = mk_pte(page, prot);
+               if (mkwrite) {
+                       entry = pte_mkyoung(entry);
+                       entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+               }
                inc_mm_counter(vma->vm_mm, mm_counter_file(folio));
                folio_add_file_rmap_pte(folio, page, vma);
        }
@@ -2147,7 +2168,7 @@ static int insert_page_into_pte_locked(struct 
vm_area_struct *vma, pte_t *pte,
 }
 
 static int insert_page(struct vm_area_struct *vma, unsigned long addr,
-                       struct page *page, pgprot_t prot)
+                       struct page *page, pgprot_t prot, bool mkwrite)
 {
        int retval;
        pte_t *pte;
@@ -2160,7 +2181,7 @@ static int insert_page(struct vm_area_struct *vma, 
unsigned long addr,
        pte = get_locked_pte(vma->vm_mm, addr, &ptl);
        if (!pte)
                goto out;
-       retval = insert_page_into_pte_locked(vma, pte, addr, page, prot);
+       retval = insert_page_into_pte_locked(vma, pte, addr, page, prot, 
mkwrite);
        pte_unmap_unlock(pte, ptl);
 out:
        return retval;
@@ -2174,7 +2195,7 @@ static int insert_page_in_batch_locked(struct 
vm_area_struct *vma, pte_t *pte,
        err = validate_page_before_insert(vma, page);
        if (err)
                return err;
-       return insert_page_into_pte_locked(vma, pte, addr, page, prot);
+       return insert_page_into_pte_locked(vma, pte, addr, page, prot, false);
 }
 
 /* insert_pages() amortizes the cost of spinlock operations
@@ -2310,7 +2331,7 @@ int vm_insert_page(struct vm_area_struct *vma, unsigned 
long addr,
                BUG_ON(vma->vm_flags & VM_PFNMAP);
                vm_flags_set(vma, VM_MIXEDMAP);
        }
-       return insert_page(vma, addr, page, vma->vm_page_prot);
+       return insert_page(vma, addr, page, vma->vm_page_prot, false);
 }
 EXPORT_SYMBOL(vm_insert_page);
 
@@ -2590,7 +2611,7 @@ static vm_fault_t __vm_insert_mixed(struct vm_area_struct 
*vma,
                 * result in pfn_t_has_page() == false.
                 */
                page = pfn_to_page(pfn_t_to_pfn(pfn));
-               err = insert_page(vma, addr, page, pgprot);
+               err = insert_page(vma, addr, page, pgprot, mkwrite);
        } else {
                return insert_pfn(vma, addr, pfn, pgprot, mkwrite);
        }
-- 
git-series 0.9.1