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, 5 insertions, 46 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 */