Provide a helper function for finishing write faults due to PTE being
read-only. The helper will be used by DAX to avoid the need of
complicating generic MM code with DAX locking specifics.
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
include/linux/mm.h | 1 +
mm/memory.c | 62 +++++++++++++++++++++++++++++++++++-------------------
2 files changed, 41 insertions(+), 22 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index daf690fccc0c..32ff572a6e6c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -601,6 +601,7 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
void do_set_pte(struct vm_area_struct *vma, unsigned long address,
struct page *page, pte_t *pte, bool write, bool anon);
int finish_fault(struct vm_area_struct *vma, struct vm_fault *vmf);
+int finish_mkwrite_fault(struct vm_area_struct *vma, struct vm_fault *vmf);
#endif
/*
diff --git a/mm/memory.c b/mm/memory.c
index 1d2916c53d43..30cf7b36df48 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2262,6 +2262,41 @@ oom:
return VM_FAULT_OOM;
}
+/**
+ * finish_mkrite_fault - finish page fault making PTE writeable once the page
+ * page is prepared
+ *
+ * @vma: virtual memory area
+ * @vmf: structure describing the fault
+ *
+ * This function handles all that is needed to finish a write page fault due
+ * to PTE being read-only once the mapped page is prepared. It handles locking
+ * of PTE and modifying it. The function returns 0 on success, error in case
+ * the PTE changed before we acquired PTE lock.
+ *
+ * The function expects the page to be locked or other protection against
+ * concurrent faults / writeback (such as DAX radix tree locks).
+ */
+int finish_mkwrite_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+ unsigned long address = (unsigned long)vmf->virtual_address;
+ pte_t *pte;
+ spinlock_t *ptl;
+
+ pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, address, &ptl);
+ /*
+ * We might have raced with another page fault while we
+ * released the pte_offset_map_lock.
+ */
+ if (!pte_same(*pte, vmf->orig_pte)) {
+ pte_unmap_unlock(pte, ptl);
+ return -EBUSY;
+ }
+ wp_page_reuse(vma->vm_mm, vma, address, pte, ptl, vmf->orig_pte,
+ vmf->page);
+ return 0;
+}
+
/*
* Handle write page faults for VM_MIXEDMAP or VM_PFNMAP for a VM_SHARED
* mapping
@@ -2282,17 +2317,12 @@ static int wp_pfn_shared(struct mm_struct *mm,
ret = vma->vm_ops->pfn_mkwrite(vma, &vmf);
if (ret & VM_FAULT_ERROR)
return ret;
- page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
- /*
- * We might have raced with another page fault while we
- * released the pte_offset_map_lock.
- */
- if (!pte_same(*page_table, orig_pte)) {
- pte_unmap_unlock(page_table, ptl);
+ if (finish_mkwrite_fault(vma, &vmf) < 0)
return 0;
- }
+ } else {
+ wp_page_reuse(mm, vma, address, page_table, ptl, orig_pte,
+ NULL);
}
- wp_page_reuse(mm, vma, address, page_table, ptl, orig_pte, NULL);
return VM_FAULT_WRITE;
}
@@ -2319,28 +2349,16 @@ static int wp_page_shared(struct mm_struct *mm, struct vm_area_struct *vma,
put_page(old_page);
return tmp;
}
- /*
- * Since we dropped the lock we need to revalidate
- * the PTE as someone else may have changed it. If
- * they did, we just return, as we can count on the
- * MMU to tell us if they didn't also make it writable.
- */
- page_table = pte_offset_map_lock(mm, pmd, address,
- &ptl);
- if (!pte_same(*page_table, orig_pte)) {
+ if (finish_mkwrite_fault(vma, &vmf) < 0) {
unlock_page(old_page);
- pte_unmap_unlock(page_table, ptl);
put_page(old_page);
return 0;
}
- wp_page_reuse(mm, vma, address, page_table, ptl, orig_pte,
- old_page);
} else {
wp_page_reuse(mm, vma, address, page_table, ptl, orig_pte,
old_page);
lock_page(old_page);
}
-
fault_dirty_shared_page(vma, old_page);
put_page(old_page);
return VM_FAULT_WRITE;
--
2.6.6
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