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Message-ID: <16481.1415991906@famine>
Date: Fri, 14 Nov 2014 11:05:06 -0800
From: Jay Vosburgh <jay.vosburgh@...onical.com>
To: David Miller <davem@...emloft.net>
cc: hannes@...essinduktion.org, eric.dumazet@...il.com,
netdev@...r.kernel.org, ogerlitz@...lanox.com, pshelar@...ira.com,
jesse@...ira.com, discuss@...nvswitch.org
Subject: [PATCH net-next] Revert "fast_hash: avoid indirect function calls"
This reverts commit e5a2c899957659cd1a9f789bc462f9c0b35f5150.
Commit e5a2c899 introduced an alternative_call, arch_fast_hash2,
that selects between __jhash2 and __intel_crc4_2_hash based on the
X86_FEATURE_XMM4_2.
Unfortunately, the alternative_call system does not appear to be
suitable for use with C functions, as register usage is not handled
properly for the called functions. The __jhash2 function in particular
clobbers registers that are not preserved when called via
alternative_call, resulting in a panic for direct callers of
arch_fast_hash2 on older CPUs lacking sse4_2. It is possible that
__intel_crc4_2_hash works merely by chance because it uses fewer
registers.
This commit was suggested as the source of the problem by Jesse
Gross <jesse@...ira.com>.
Signed-off-by: Jay Vosburgh <jay.vosburgh@...onical.com>
---
arch/x86/include/asm/hash.h | 51 +++++----------------------------------------
arch/x86/lib/hash.c | 29 +++++++++++---------------
include/asm-generic/hash.h | 36 ++------------------------------
include/linux/hash.h | 34 ++++++++++++++++++++++++++++++
lib/Makefile | 2 +-
lib/hash.c | 39 ++++++++++++++++++++++++++++++++++
6 files changed, 93 insertions(+), 98 deletions(-)
create mode 100644 lib/hash.c
diff --git a/arch/x86/include/asm/hash.h b/arch/x86/include/asm/hash.h
index a881d78..e8c58f8 100644
--- a/arch/x86/include/asm/hash.h
+++ b/arch/x86/include/asm/hash.h
@@ -1,48 +1,7 @@
-#ifndef __ASM_X86_HASH_H
-#define __ASM_X86_HASH_H
+#ifndef _ASM_X86_HASH_H
+#define _ASM_X86_HASH_H
-#include <linux/cpufeature.h>
-#include <asm/alternative.h>
+struct fast_hash_ops;
+extern void setup_arch_fast_hash(struct fast_hash_ops *ops);
-u32 __intel_crc4_2_hash(const void *data, u32 len, u32 seed);
-u32 __intel_crc4_2_hash2(const u32 *data, u32 len, u32 seed);
-
-/*
- * non-inline versions of jhash so gcc does not need to generate
- * duplicate code in every object file
- */
-u32 __jhash(const void *data, u32 len, u32 seed);
-u32 __jhash2(const u32 *data, u32 len, u32 seed);
-
-/*
- * for documentation of these functions please look into
- * <include/asm-generic/hash.h>
- */
-
-static inline u32 arch_fast_hash(const void *data, u32 len, u32 seed)
-{
- u32 hash;
-
- alternative_call(__jhash, __intel_crc4_2_hash, X86_FEATURE_XMM4_2,
-#ifdef CONFIG_X86_64
- "=a" (hash), "D" (data), "S" (len), "d" (seed));
-#else
- "=a" (hash), "a" (data), "d" (len), "c" (seed));
-#endif
- return hash;
-}
-
-static inline u32 arch_fast_hash2(const u32 *data, u32 len, u32 seed)
-{
- u32 hash;
-
- alternative_call(__jhash2, __intel_crc4_2_hash2, X86_FEATURE_XMM4_2,
-#ifdef CONFIG_X86_64
- "=a" (hash), "D" (data), "S" (len), "d" (seed));
-#else
- "=a" (hash), "a" (data), "d" (len), "c" (seed));
-#endif
- return hash;
-}
-
-#endif /* __ASM_X86_HASH_H */
+#endif /* _ASM_X86_HASH_H */
diff --git a/arch/x86/lib/hash.c b/arch/x86/lib/hash.c
index e143271..ff4fa51 100644
--- a/arch/x86/lib/hash.c
+++ b/arch/x86/lib/hash.c
@@ -31,13 +31,13 @@
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
+#include <linux/hash.h>
+#include <linux/init.h>
+
#include <asm/processor.h>
#include <asm/cpufeature.h>
#include <asm/hash.h>
-#include <linux/hash.h>
-#include <linux/jhash.h>
-
static inline u32 crc32_u32(u32 crc, u32 val)
{
#ifdef CONFIG_AS_CRC32
@@ -48,7 +48,7 @@ static inline u32 crc32_u32(u32 crc, u32 val)
return crc;
}
-u32 __intel_crc4_2_hash(const void *data, u32 len, u32 seed)
+static u32 intel_crc4_2_hash(const void *data, u32 len, u32 seed)
{
const u32 *p32 = (const u32 *) data;
u32 i, tmp = 0;
@@ -71,27 +71,22 @@ u32 __intel_crc4_2_hash(const void *data, u32 len, u32 seed)
return seed;
}
-EXPORT_SYMBOL(__intel_crc4_2_hash);
-u32 __intel_crc4_2_hash2(const u32 *data, u32 len, u32 seed)
+static u32 intel_crc4_2_hash2(const u32 *data, u32 len, u32 seed)
{
+ const u32 *p32 = (const u32 *) data;
u32 i;
for (i = 0; i < len; i++)
- seed = crc32_u32(seed, *data++);
+ seed = crc32_u32(seed, *p32++);
return seed;
}
-EXPORT_SYMBOL(__intel_crc4_2_hash2);
-u32 __jhash(const void *data, u32 len, u32 seed)
+void __init setup_arch_fast_hash(struct fast_hash_ops *ops)
{
- return jhash(data, len, seed);
-}
-EXPORT_SYMBOL(__jhash);
-
-u32 __jhash2(const u32 *data, u32 len, u32 seed)
-{
- return jhash2(data, len, seed);
+ if (cpu_has_xmm4_2) {
+ ops->hash = intel_crc4_2_hash;
+ ops->hash2 = intel_crc4_2_hash2;
+ }
}
-EXPORT_SYMBOL(__jhash2);
diff --git a/include/asm-generic/hash.h b/include/asm-generic/hash.h
index 3c82760..b631284 100644
--- a/include/asm-generic/hash.h
+++ b/include/asm-generic/hash.h
@@ -1,41 +1,9 @@
#ifndef __ASM_GENERIC_HASH_H
#define __ASM_GENERIC_HASH_H
-#include <linux/jhash.h>
-
-/**
- * arch_fast_hash - Caclulates a hash over a given buffer that can have
- * arbitrary size. This function will eventually use an
- * architecture-optimized hashing implementation if
- * available, and trades off distribution for speed.
- *
- * @data: buffer to hash
- * @len: length of buffer in bytes
- * @seed: start seed
- *
- * Returns 32bit hash.
- */
-static inline u32 arch_fast_hash(const void *data, u32 len, u32 seed)
-{
- return jhash(data, len, seed);
-}
-
-/**
- * arch_fast_hash2 - Caclulates a hash over a given buffer that has a
- * size that is of a multiple of 32bit words. This
- * function will eventually use an architecture-
- * optimized hashing implementation if available,
- * and trades off distribution for speed.
- *
- * @data: buffer to hash (must be 32bit padded)
- * @len: number of 32bit words
- * @seed: start seed
- *
- * Returns 32bit hash.
- */
-static inline u32 arch_fast_hash2(const u32 *data, u32 len, u32 seed)
+struct fast_hash_ops;
+static inline void setup_arch_fast_hash(struct fast_hash_ops *ops)
{
- return jhash2(data, len, seed);
}
#endif /* __ASM_GENERIC_HASH_H */
diff --git a/include/linux/hash.h b/include/linux/hash.h
index 6e8fb02..d0494c3 100644
--- a/include/linux/hash.h
+++ b/include/linux/hash.h
@@ -84,4 +84,38 @@ static inline u32 hash32_ptr(const void *ptr)
return (u32)val;
}
+struct fast_hash_ops {
+ u32 (*hash)(const void *data, u32 len, u32 seed);
+ u32 (*hash2)(const u32 *data, u32 len, u32 seed);
+};
+
+/**
+ * arch_fast_hash - Caclulates a hash over a given buffer that can have
+ * arbitrary size. This function will eventually use an
+ * architecture-optimized hashing implementation if
+ * available, and trades off distribution for speed.
+ *
+ * @data: buffer to hash
+ * @len: length of buffer in bytes
+ * @seed: start seed
+ *
+ * Returns 32bit hash.
+ */
+extern u32 arch_fast_hash(const void *data, u32 len, u32 seed);
+
+/**
+ * arch_fast_hash2 - Caclulates a hash over a given buffer that has a
+ * size that is of a multiple of 32bit words. This
+ * function will eventually use an architecture-
+ * optimized hashing implementation if available,
+ * and trades off distribution for speed.
+ *
+ * @data: buffer to hash (must be 32bit padded)
+ * @len: number of 32bit words
+ * @seed: start seed
+ *
+ * Returns 32bit hash.
+ */
+extern u32 arch_fast_hash2(const u32 *data, u32 len, u32 seed);
+
#endif /* _LINUX_HASH_H */
diff --git a/lib/Makefile b/lib/Makefile
index 04e53dd..7512dc9 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -26,7 +26,7 @@ obj-y += bcd.o div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \
bust_spinlocks.o hexdump.o kasprintf.o bitmap.o scatterlist.o \
gcd.o lcm.o list_sort.o uuid.o flex_array.o iovec.o clz_ctz.o \
bsearch.o find_last_bit.o find_next_bit.o llist.o memweight.o kfifo.o \
- percpu-refcount.o percpu_ida.o rhashtable.o
+ percpu-refcount.o percpu_ida.o hash.o rhashtable.o
obj-y += string_helpers.o
obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
obj-y += kstrtox.o
diff --git a/lib/hash.c b/lib/hash.c
new file mode 100644
index 0000000..fea973f
--- /dev/null
+++ b/lib/hash.c
@@ -0,0 +1,39 @@
+/* General purpose hashing library
+ *
+ * That's a start of a kernel hashing library, which can be extended
+ * with further algorithms in future. arch_fast_hash{2,}() will
+ * eventually resolve to an architecture optimized implementation.
+ *
+ * Copyright 2013 Francesco Fusco <ffusco@...hat.com>
+ * Copyright 2013 Daniel Borkmann <dborkman@...hat.com>
+ * Copyright 2013 Thomas Graf <tgraf@...hat.com>
+ * Licensed under the GNU General Public License, version 2.0 (GPLv2)
+ */
+
+#include <linux/jhash.h>
+#include <linux/hash.h>
+#include <linux/cache.h>
+
+static struct fast_hash_ops arch_hash_ops __read_mostly = {
+ .hash = jhash,
+ .hash2 = jhash2,
+};
+
+u32 arch_fast_hash(const void *data, u32 len, u32 seed)
+{
+ return arch_hash_ops.hash(data, len, seed);
+}
+EXPORT_SYMBOL_GPL(arch_fast_hash);
+
+u32 arch_fast_hash2(const u32 *data, u32 len, u32 seed)
+{
+ return arch_hash_ops.hash2(data, len, seed);
+}
+EXPORT_SYMBOL_GPL(arch_fast_hash2);
+
+static int __init hashlib_init(void)
+{
+ setup_arch_fast_hash(&arch_hash_ops);
+ return 0;
+}
+early_initcall(hashlib_init);
--
1.9.1
--
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