This is a note to let you know that I've just added the patch titled
lib/bitmap: drop optimization of bitmap_{from,to}_arr64
to the 6.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
lib-bitmap-drop-optimization-of-bitmap_-from-to-_arr.patch
and it can be found in the queue-6.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 652c15b135e8e0e0922f7097ec5eebbed6966040
Author: Yury Norov <yury.norov@xxxxxxxxx>
Date: Mon Feb 27 11:24:36 2023 -0800
lib/bitmap: drop optimization of bitmap_{from,to}_arr64
[ Upstream commit c1d2ba10f594046831d14b03f194e8d05e78abad ]
bitmap_{from,to}_arr64() optimization is overly optimistic on 32-bit LE
architectures when it's wired to bitmap_copy_clear_tail().
bitmap_copy_clear_tail() takes care of unused bits in the bitmap up to
the next word boundary. But on 32-bit machines when copying bits from
bitmap to array of 64-bit words, it's expected that the unused part of
a recipient array must be cleared up to 64-bit boundary, so the last 4
bytes may stay untouched when nbits % 64 <= 32.
While the copying part of the optimization works correct, that clear-tail
trick makes corresponding tests reasonably fail:
test_bitmap: bitmap_to_arr64(nbits == 1): tail is not safely cleared: 0xa5a5a5a500000001 (must be 0x0000000000000001)
Fix it by removing bitmap_{from,to}_arr64() optimization for 32-bit LE
arches.
Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Link: https://lore.kernel.org/lkml/20230225184702.GA3587246@xxxxxxxxxxxx/
Fixes: 0a97953fd221 ("lib: add bitmap_{from,to}_arr64")
Signed-off-by: Yury Norov <yury.norov@xxxxxxxxx>
Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Reviewed-by: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 7d6d73b781472..03644237e1efb 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -302,12 +302,10 @@ void bitmap_to_arr32(u32 *buf, const unsigned long *bitmap,
#endif
/*
- * On 64-bit systems bitmaps are represented as u64 arrays internally. On LE32
- * machines the order of hi and lo parts of numbers match the bitmap structure.
- * In both cases conversion is not needed when copying data from/to arrays of
- * u64.
+ * On 64-bit systems bitmaps are represented as u64 arrays internally. So,
+ * the conversion is not needed when copying data from/to arrays of u64.
*/
-#if (BITS_PER_LONG == 32) && defined(__BIG_ENDIAN)
+#if BITS_PER_LONG == 32
void bitmap_from_arr64(unsigned long *bitmap, const u64 *buf, unsigned int nbits);
void bitmap_to_arr64(u64 *buf, const unsigned long *bitmap, unsigned int nbits);
#else
diff --git a/lib/bitmap.c b/lib/bitmap.c
index 1c81413c51f86..ddb31015e38ae 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -1495,7 +1495,7 @@ void bitmap_to_arr32(u32 *buf, const unsigned long *bitmap, unsigned int nbits)
EXPORT_SYMBOL(bitmap_to_arr32);
#endif
-#if (BITS_PER_LONG == 32) && defined(__BIG_ENDIAN)
+#if BITS_PER_LONG == 32
/**
* bitmap_from_arr64 - copy the contents of u64 array of bits to bitmap
* @bitmap: array of unsigned longs, the destination bitmap
