[v2]
Based on linux-next/akpm [3dc4623]. For v4.1 merge window
Incorporated comments from Andrew And Kirill
[v1]
This will allow FS that uses VM_PFNMAP | VM_MIXEDMAP (no page structs)
to get notified when access is a write to a read-only PFN.
This can happen if we mmap() a file then first mmap-read from it
to page-in a read-only PFN, than we mmap-write to the same page.
We need this functionality to fix a DAX bug, where in the scenario
above we fail to set ctime/mtime though we modified the file.
An xfstest is attached to this patchset that shows the failure
and the fix. (A DAX patch will follow)
This functionality is extra important for us, because upon
dirtying of a pmem page we also want to RDMA the page to a
remote cluster node.
We define a new pfn_mkwrite and do not reuse page_mkwrite because
1 - The name ;-)
2 - But mainly because it would take a very long and tedious
audit of all page_mkwrite functions of VM_MIXEDMAP/VM_PFNMAP
users. To make sure they do not now CRASH. For example current
DAX code (which this is for) would crash.
If we would want to reuse page_mkwrite, We will need to first
patch all users, so to not-crash-on-no-page. Then enable this
patch. But even if I did that I would not sleep so well at night.
Adding a new vector is the safest thing to do, and is not that
expensive. an extra pointer at a static function vector per driver.
Also the new vector is better for performance, because else we
Will call all current Kernel vectors, so to:
check-ha-no-page-do-nothing and return.
No need to call it from do_shared_fault because do_wp_page is called to
change pte permissions anyway.
CC: Matthew Wilcox <matthew.r.wilcox@xxxxxxxxx>
CC: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
CC: Jan Kara <jack@xxxxxxx>
CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
CC: Hugh Dickins <hughd@xxxxxxxxxx>
CC: Mel Gorman <mgorman@xxxxxxx>
CC: linux-mm@xxxxxxxxx
Signed-off-by: Yigal Korman <yigal@xxxxxxxxxxxxx>
Signed-off-by: Boaz Harrosh <boaz@xxxxxxxxxxxxx>
---
include/linux/mm.h | 3 +++
mm/memory.c | 35 +++++++++++++++++++++++++++++++----
2 files changed, 34 insertions(+), 4 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index d584b95..70c47f2 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -251,6 +251,9 @@ 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);
+ /* same as page_mkwrite when using VM_PFNMAP|VM_MIXEDMAP */
+ 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 59f6268..6e8f3f6 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1982,6 +1982,19 @@ static int do_page_mkwrite(struct vm_area_struct *vma, struct page *page,
return ret;
}
+static int do_pfn_mkwrite(struct vm_area_struct *vma, unsigned long address)
+{
+ struct vm_fault vmf = {
+ .page = 0,
+ .pgoff = (((address & PAGE_MASK) - vma->vm_start)
+ >> PAGE_SHIFT) + vma->vm_pgoff,
+ .virtual_address = (void __user *)(address & PAGE_MASK),
+ .flags = FAULT_FLAG_WRITE | FAULT_FLAG_MKWRITE,
+ };
+
+ return vma->vm_ops->pfn_mkwrite(vma, &vmf);
+}
+
/*
* Handle write page faults for pages that can be reused in the current vma
*
@@ -2259,14 +2272,28 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
* VM_PFNMAP VMA.
*
* 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.
+ * Just mark the pages writable and/or call ops->pfn_mkwrite.
*/
if ((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
- (VM_WRITE|VM_SHARED))
+ (VM_WRITE|VM_SHARED)) {
+ if (vma->vm_ops && vma->vm_ops->pfn_mkwrite) {
+ int ret;
+
+ pte_unmap_unlock(page_table, ptl);
+ ret = do_pfn_mkwrite(vma, address);
+ if (ret & VM_FAULT_ERROR)
+ return ret;
+ page_table = pte_offset_map_lock(mm, pmd,
+ address, &ptl);
+ /* Did pfn_mkwrite already fixed up the pte */
+ if (!pte_same(*page_table, orig_pte)) {
+ pte_unmap_unlock(page_table, ptl);
+ return ret;
+ }
+ }
return wp_page_reuse(mm, vma, address, page_table, ptl,
orig_pte, old_page, 0, 0);
-
+ }
pte_unmap_unlock(page_table, ptl);
return wp_page_copy(mm, vma, address, page_table, pmd,
orig_pte, old_page);
--
1.9.3
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