Revert "fast_hash: avoid indirect function calls"

This reverts commit e5a2c89995.

	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>
This commit is contained in:
Jay Vosburgh 2014-11-14 11:05:06 -08:00 committed by David S. Miller
parent 8cd4313aa7
commit a77f9c5dcd
6 changed files with 93 additions and 98 deletions

View File

@ -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 */

View File

@ -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);
if (cpu_has_xmm4_2) {
ops->hash = intel_crc4_2_hash;
ops->hash2 = intel_crc4_2_hash2;
}
}
EXPORT_SYMBOL(__jhash);
u32 __jhash2(const u32 *data, u32 len, u32 seed)
{
return jhash2(data, len, seed);
}
EXPORT_SYMBOL(__jhash2);

View File

@ -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)
struct fast_hash_ops;
static inline void setup_arch_fast_hash(struct fast_hash_ops *ops)
{
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)
{
return jhash2(data, len, seed);
}
#endif /* __ASM_GENERIC_HASH_H */

View File

@ -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 */

View File

@ -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

39
lib/hash.c Normal file
View File

@ -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@redhat.com>
* Copyright 2013 Daniel Borkmann <dborkman@redhat.com>
* Copyright 2013 Thomas Graf <tgraf@redhat.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);