[PATCH v13 3/5] mm/hwpoison: return -EFAULT when copy fail in copy_mc_[user]_highpage()

[Tong Tiangen]

Currently, copy_mc_[user]_highpage() returns zero on success, or in case
of failures, the number of bytes that weren't copied.

While tracking the number of not copied works fine for x86 and PPC, There
are some difficulties in doing the same thing on ARM64 because there is no
available caller-saved register in copy_page()(lib/copy_page.S) to save
"bytes not copied", and the following copy_mc_page() will also encounter
the same problem.

Consider the caller of copy_mc_[user]_highpage() cannot do any processing
on the remaining data(The page has hardware errors), they only check if
copy was succeeded or not, make the interface more generic by using an
error code when copy fails (-EFAULT) or return zero on success.

Signed-off-by: Tong Tiangen <tongtiangen at huawei.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron at huawei.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab+huawei at kernel.org>
---
 include/linux/highmem.h | 8 ++++----
 mm/khugepaged.c         | 4 ++--
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 6e452bd8e7e3..0eb4b9b06837 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -329,8 +329,8 @@ static inline void copy_highpage(struct page *to, struct page *from)
 /*
  * If architecture supports machine check exception handling, define the
  * #MC versions of copy_user_highpage and copy_highpage. They copy a memory
- * page with #MC in source page (@from) handled, and return the number
- * of bytes not copied if there was a #MC, otherwise 0 for success.
+ * page with #MC in source page (@from) handled, and return -EFAULT if there
+ * was a #MC, otherwise 0 for success.
  */
 static inline int copy_mc_user_highpage(struct page *to, struct page *from,
 					unsigned long vaddr, struct vm_area_struct *vma)
@@ -349,7 +349,7 @@ static inline int copy_mc_user_highpage(struct page *to, struct page *from,
 	if (ret)
 		memory_failure_queue(page_to_pfn(from), 0);
 
-	return ret;
+	return ret ? -EFAULT : 0;
 }
 
 static inline int copy_mc_highpage(struct page *to, struct page *from)
@@ -368,7 +368,7 @@ static inline int copy_mc_highpage(struct page *to, struct page *from)
 	if (ret)
 		memory_failure_queue(page_to_pfn(from), 0);
 
-	return ret;
+	return ret ? -EFAULT : 0;
 }
 #else
 static inline int copy_mc_user_highpage(struct page *to, struct page *from,
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 6f8d46d107b4..c3cdc0155dcd 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -820,7 +820,7 @@ static int __collapse_huge_page_copy(pte_t *pte, struct folio *folio,
 			continue;
 		}
 		src_page = pte_page(pteval);
-		if (copy_mc_user_highpage(page, src_page, src_addr, vma) > 0) {
+		if (copy_mc_user_highpage(page, src_page, src_addr, vma)) {
 			result = SCAN_COPY_MC;
 			break;
 		}
@@ -2081,7 +2081,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
 		}
 
 		for (i = 0; i < nr_pages; i++) {
-			if (copy_mc_highpage(dst, folio_page(folio, i)) > 0) {
+			if (copy_mc_highpage(dst, folio_page(folio, i))) {
 				result = SCAN_COPY_MC;
 				goto rollback;
 			}
-- 
2.25.1