linux-kernel - [PATCH] mm/highmem: Delete memmove

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Date:   Mon,  6 Jun 2022 16:15:33 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Ira Weiny <ira.weiny@...el.com>
Subject: [PATCH] mm/highmem: Delete memmove_page()

Matthew Wilcox reported that, while he was looking at memmove_page(), he
realized that it can't actually work.

The reasons are hidden in its implementation, which makes use of
memmove() on logical addresses provided by kmap_local_page(). memmove()
does the wrong thing when it tests "if (dest <= src)".

Therefore, delete memmove_page().

No need to change any other code because we have no call sites of
memmove_page() across the whole kernel.

Reported-by: Matthew Wilcox <willy@...radead.org>
Cc: Ira Weiny <ira.weiny@...el.com>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
---
 include/linux/highmem.h | 13 -------------
 1 file changed, 13 deletions(-)

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 3af34de54330..fee9835e3793 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -336,19 +336,6 @@ static inline void memcpy_page(struct page *dst_page, size_t dst_off,
 	kunmap_local(dst);
 }
 
-static inline void memmove_page(struct page *dst_page, size_t dst_off,
-			       struct page *src_page, size_t src_off,
-			       size_t len)
-{
-	char *dst = kmap_local_page(dst_page);
-	char *src = kmap_local_page(src_page);
-
-	VM_BUG_ON(dst_off + len > PAGE_SIZE || src_off + len > PAGE_SIZE);
-	memmove(dst + dst_off, src + src_off, len);
-	kunmap_local(src);
-	kunmap_local(dst);
-}
-
 static inline void memset_page(struct page *page, size_t offset, int val,
 			       size_t len)
 {
-- 
2.36.1