linux-kernel - [PATCH 2/4] lib: add bitmap_{from,to}

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Date:   Wed, 20 Apr 2022 15:25:28 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     linux-kernel@...r.kernel.org,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Yury Norov <yury.norov@...il.com>, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org
Subject: [PATCH 2/4] lib: add bitmap_{from,to}_arr64

Manipulating 64-bit arrays with bitmap functions is potentially dangerous
because on 32-bit BE machines the order of halfwords doesn't match. Another
issue is that compiler may throw a warning about out-of-boundary access.

This patch adds bitmap_{from,to}_arr64 functions in addition to existing
bitmap_{from,to}_arr32.

Signed-off-by: Yury Norov <yury.norov@...il.com>
---
 include/linux/bitmap.h | 23 +++++++++++++++++----
 lib/bitmap.c           | 47 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+), 4 deletions(-)

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 10d805c2893c..f78c534fb814 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -292,6 +292,24 @@ void bitmap_to_arr32(u32 *buf, const unsigned long *bitmap,
 			(const unsigned long *) (bitmap), (nbits))
 #endif
 
+/*
+ * On 64-bit systems bitmaps are represented as u64 arrays internally. On LE32
+ * machines the order of hi and lo parts of nubmers match the bitmap structure.
+ * In both cases conversion is not needed when copying data from/to arrays of
+ * u64.
+ */
+#if (BITS_PER_LONG == 32) && defined(__BIG_ENDIAN)
+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
+#define bitmap_from_arr64(bitmap, buf, nbits)			\
+	bitmap_copy_clear_tail((unsigned long *) (bitmap),	\
+			(const unsigned long *) (buf), (nbits))
+#define bitmap_to_arr64(buf, bitmap, nbits)			\
+	bitmap_copy_clear_tail((unsigned long *) (buf),		\
+			(const unsigned long *) (bitmap), (nbits))
+#endif
+
 static inline int bitmap_and(unsigned long *dst, const unsigned long *src1,
 			const unsigned long *src2, unsigned int nbits)
 {
@@ -596,10 +614,7 @@ static inline void bitmap_next_set_region(unsigned long *bitmap,
  */
 static inline void bitmap_from_u64(unsigned long *dst, u64 mask)
 {
-	dst[0] = mask & ULONG_MAX;
-
-	if (sizeof(mask) > sizeof(unsigned long))
-		dst[1] = mask >> 32;
+	bitmap_from_arr64(dst, &mask, 64);
 }
 
 /**
diff --git a/lib/bitmap.c b/lib/bitmap.c
index d9a4480af5b9..aea9493f4216 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -1533,5 +1533,52 @@ void bitmap_to_arr32(u32 *buf, const unsigned long *bitmap, unsigned int nbits)
 		buf[halfwords - 1] &= (u32) (UINT_MAX >> ((-nbits) & 31));
 }
 EXPORT_SYMBOL(bitmap_to_arr32);
+#endif
+
+#if (BITS_PER_LONG == 32) && defined(__BIG_ENDIAN)
+/**
+ * bitmap_from_arr64 - copy the contents of u64 array of bits to bitmap
+ *	@bitmap: array of unsigned longs, the destination bitmap
+ *	@buf: array of u64 (in host byte order), the source bitmap
+ *	@nbits: number of bits in @bitmap
+ */
+void bitmap_from_arr64(unsigned long *bitmap, const u64 *buf, unsigned int nbits)
+{
+	while (nbits > 0) {
+		u64 val = *buf++;
+
+		*bitmap++ = (unsigned long)val;
+		if (nbits > 32)
+			*bitmap++ = (unsigned long)(val >> 32);
+		nbits -= 64;
+	}
 
+	/* Clear tail bits in last word beyond nbits. */
+	if (nbits % BITS_PER_LONG)
+		bitmap[-1] &= BITMAP_LAST_WORD_MASK(nbits);
+}
+EXPORT_SYMBOL(bitmap_from_arr64);
+
+/**
+ * bitmap_to_arr64 - copy the contents of bitmap to a u64 array of bits
+ *	@buf: array of u64 (in host byte order), the dest bitmap
+ *	@bitmap: array of unsigned longs, the source bitmap
+ *	@nbits: number of bits in @bitmap
+ */
+void bitmap_to_arr64(u64 *buf, const unsigned long *bitmap, unsigned int nbits)
+{
+	unsigned long *end = bitmap + BITS_TO_LONGS(nbits);
+
+	while (bitmap < end) {
+		*buf = *bitmap++;
+		if (bitmap < end)
+			*buf |= *bitmap++ << 32;
+		buf++;
+	}
+
+	/* Clear tail bits in last element of array beyond nbits. */
+	if (nbits % 64)
+		buf[-1] &= GENMASK_ULL(nbits, 0);
+}
+EXPORT_SYMBOL(bitmap_to_arr64);
 #endif
-- 
2.32.0