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>

1 files changed, 34 insertions, 0 deletions

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);
+};
+
+/**
+ *      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 */