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@nicira.com>.

Signed-off-by: Jay Vosburgh <jay.vosburgh@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

6 files changed, 93 insertions, 98 deletions

diff --git a/arch/x86/include/asm/hash.h b/arch/x86/include/asm/hash.h
index a881d784f044..e8c58f88b1d4 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 e14327198835..ff4fa51a5b1f 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 3c82760ff2a4..b6312843dbd9 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 6e8fb028848c..d0494c399392 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);
+};
+