A callback similar to page_mkwrite except it will be called before making
ptes that don't point to normal pages writable.
Signed-off-by: Thomas Hellstrom <thellstrom@xxxxxxxxxx>
---
include/linux/mm.h | 9 +++++++++
mm/memory.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++++---
2 files changed, 58 insertions(+), 3 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 8b6e55e..23d1791 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -212,6 +212,15 @@ struct vm_operations_struct {
* writable, if an error is returned it will cause a SIGBUS */
int (*page_mkwrite)(struct vm_area_struct *vma, struct vm_fault *vmf);
+ /*
+ * Notification that a previously read-only pfn map is about to become
+ * writable, Returning VM_FAULT_NOPAGE will cause the fault to be
+ * retried,
+ * Returning a VM_FAULT_SIGBUS or VM_FAULT_OOM will propagate the
+ * error. Returning 0 will make the pfn map writable.
+ */
+ int (*pfn_mkwrite)(struct vm_area_struct *vma, struct vm_fault *vmf);
+
/* called by access_process_vm when get_user_pages() fails, typically
* for use by special VMAs that can switch between memory and hardware
*/
diff --git a/mm/memory.c b/mm/memory.c
index d176154..8ae9a6e 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2584,6 +2584,45 @@ static inline void cow_user_page(struct page *dst, struct page *src, unsigned lo
copy_user_highpage(dst, src, va, vma);
}
+static int prepare_call_pfn_mkwrite(struct vm_area_struct *vma,
+ unsigned long address,
+ pte_t *pte, pmd_t *pmd,
+ spinlock_t *ptl, pte_t orig_pte)
+{
+ int ret = 0;
+ struct vm_fault vmf;
+ struct mm_struct *mm = vma->vm_mm;
+
+ if (!vma->vm_ops || !vma->vm_ops->pfn_mkwrite)
+ return 0;
+
+ /*
+ * In general, we can't say anything about the mapping offset
+ * here, so set it to 0.
+ */
+ vmf.pgoff = 0;
+ vmf.virtual_address = (void __user *)(address & PAGE_MASK);
+ vmf.flags = FAULT_FLAG_WRITE | FAULT_FLAG_MKWRITE;
+ vmf.page = NULL;
+ pte_unmap_unlock(pte, ptl);
+ ret = vma->vm_ops->pfn_mkwrite(vma, &vmf);
+ if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))
+ return ret;
+
+ pte = pte_offset_map_lock(mm, pmd, address, &ptl);
+
+ /*
+ * Retry the fault if someone updated the pte while we
+ * dropped the lock.
+ */
+ if (!pte_same(*pte, orig_pte)) {
+ pte_unmap_unlock(pte, ptl);
+ return VM_FAULT_NOPAGE;
+ }
+
+ return 0;
+}
+
/*
* This routine handles present pages, when users try to write
* to a shared page. It is done by copying the page to a new address
@@ -2621,12 +2660,19 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
* VM_MIXEDMAP !pfn_valid() case
*
* We should not cow pages in a shared writeable mapping.
- * Just mark the pages writable as we can't do any dirty
- * accounting on raw pfn maps.
+ * Optionally call pfn_mkwrite to notify the address
+ * space that the pte is about to become writeable.
*/
if ((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
- (VM_WRITE|VM_SHARED))
+ (VM_WRITE|VM_SHARED)) {
+ ret = prepare_call_pfn_mkwrite(vma, address,
+ page_table, pmd, ptl,
+ orig_pte);
+ if (ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE))
+ return ret;
+
goto reuse;
+ }
goto gotten;
}
--
1.7.10.4
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