[PATCH v8 12/20] mm/memory: Enhance insert_page_into_pte_locked() to create writable mappings

Alistair Popple
2025-02-18T03:56:58Z

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 <dan.j.williams@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: David Hildenbrand <david@redhat.com>

---

Changes for v7:
- Drop entry and reuse pteval as suggested by David.

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 | 39 ++++++++++++++++++++++++++++++---------
1 file changed, 30 insertions(+), 9 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 905ed2f..becfaf4 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2126,19 +2126,39 @@ 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 pteval;
+ pte_t pteval = ptep_get(pte);
+
+ if (!pte_none(pteval)) {
+ if (!mkwrite)
+ return -EBUSY;
+
+ /* see insert_pfn(). */
+ if (pte_pfn(pteval) != page_to_pfn(page)) {
+ WARN_ON_ONCE(!is_zero_pfn(pte_pfn(pteval)));
+ return -EFAULT;
+ }
+ pteval = maybe_mkwrite(pteval, vma);
+ pteval = pte_mkyoung(pteval);
+ if (ptep_set_access_flags(vma, addr, pte, pteval, 1))
+ update_mmu_cache(vma, addr, pte);
+ return 0;
+ }

- if (!pte_none(ptep_get(pte)))
- return -EBUSY;
/* 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);
+ pteval = mk_pte(page, prot);
+ if (mkwrite) {
+ pteval = pte_mkyoung(pteval);
+ pteval = maybe_mkwrite(pte_mkdirty(pteval), vma);
+ }
inc_mm_counter(vma->vm_mm, mm_counter_file(folio));
folio_add_file_rmap_pte(folio, page, vma);
}
@@ -2147,7 +2167,7 @@ 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 +2180,8 @@ 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);
}
--
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