Using %rbp as a temporary register breaks frame pointer convention and
breaks stack traces when unwinding from an interrupt in the crypto code.
In twofish-3way, we can't simply replace %rbp with another register
because there are none available. Instead, we use the stack to hold the
values that %rbp, %r11, and %r12 were holding previously. Each of these
values represents the half of the output from the previous Feistel round
that is being passed on unchanged to the following round. They are only
used once per round, when they are exchanged with %rax, %rbx, and %rcx.
As a result, we free up 3 registers (one per block) and can reassign
them so that %rbp is not used, and additionally %r14 and %r15 are not
used so they do not need to be saved/restored.
There may be a small overhead caused by replacing 'xchg REG, REG' with
the needed sequence 'mov MEM, REG; mov REG, MEM; mov REG, REG' once per
round. But, counterintuitively, when I tested "ctr-twofish-3way" on a
Haswell processor, the new version was actually about 2% faster.
(Perhaps 'xchg' is not as well optimized as plain moves.)
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Patch adds 3-way parallel x86_64 assembly implementation of twofish as new
module. New assembler functions crypt data in three blocks chunks, improving
cipher performance on out-of-order CPUs.
Patch has been tested with tcrypt and automated filesystem tests.
Summary of the tcrypt benchmarks:
Twofish 3-way-asm vs twofish asm (128bit 8kb block ECB)
encrypt: 1.3x speed
decrypt: 1.3x speed
Twofish 3-way-asm vs twofish asm (128bit 8kb block CBC)
encrypt: 1.07x speed
decrypt: 1.4x speed
Twofish 3-way-asm vs twofish asm (128bit 8kb block CTR)
encrypt: 1.4x speed
Twofish 3-way-asm vs AES asm (128bit 8kb block ECB)
encrypt: 1.0x speed
decrypt: 1.0x speed
Twofish 3-way-asm vs AES asm (128bit 8kb block CBC)
encrypt: 0.84x speed
decrypt: 1.09x speed
Twofish 3-way-asm vs AES asm (128bit 8kb block CTR)
encrypt: 1.15x speed
Full output:
http://koti.mbnet.fi/axh/kernel/crypto/tcrypt-speed-twofish-3way-asm-x86_64.txthttp://koti.mbnet.fi/axh/kernel/crypto/tcrypt-speed-twofish-asm-x86_64.txthttp://koti.mbnet.fi/axh/kernel/crypto/tcrypt-speed-aes-asm-x86_64.txt
Tests were run on:
vendor_id : AuthenticAMD
cpu family : 16
model : 10
model name : AMD Phenom(tm) II X6 1055T Processor
Also userspace test were run on:
vendor_id : GenuineIntel
cpu family : 6
model : 15
model name : Intel(R) Xeon(R) CPU E7330 @ 2.40GHz
stepping : 11
Userspace test results:
Encryption/decryption of twofish 3-way vs x86_64-asm on AMD Phenom II:
encrypt: 1.27x
decrypt: 1.25x
Encryption/decryption of twofish 3-way vs x86_64-asm on Intel Xeon E7330:
encrypt: 1.36x
decrypt: 1.36x
Signed-off-by: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
