[PATCH v3 12/25] mm/memory: Enhance insert_page_into_pte_locked() to create writable mappings

Alistair Popple
2024-11-22T01:46:43Z

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>

---

Changes since v2:

- New patch split out from "mm/memory: Add dax_insert_pfn"
---
mm/memory.c | 45 +++++++++++++++++++++++++++++++++++++--------
1 file changed, 37 insertions(+), 8 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 24a34a4..323662c 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2042,19 +2042,47 @@ 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;
+
+ /*
+ * For read faults on private mappings the PFN passed in may not
+ * match the PFN we have mapped if the mapped PFN is a writeable
+ * COW page. In the mkwrite case we are creating a writable PTE
+ * for a shared mapping and we expect the PFNs to match. If they
+ * don't match, we are likely racing with block allocation and
+ * mapping invalidation so just skip the update.
+ */
+ 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);
}
@@ -2063,7 +2091,7 @@ 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;
@@ -2076,7 +2104,8 @@ 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;
@@ -2090,7 +2119,7 @@ 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
@@ -2226,7 +2255,7 @@ 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);

@@ -2506,7 +2535,7 @@ 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