dm crypt: log the encryption algorithm implementation

From: Eric Biggers <[email protected]>

Log the encryption algorithm's driver name when a dm-crypt target is created. This will help people determine whether the expected implementation is being used. In some cases we've seen people do benchmarks and reject using encryption for performance reasons, when in fact they used a much slower implementation than was possible on the hardware. It can make an enormous difference; e.g., AES-XTS on ARM can be over 10x faster with the crypto extensions than without. It can also be useful to know if an implementation using an external crypto accelerator is being used instead of a software implementation.

Example message:

[   29.307629] device-mapper: crypt: xts(aes) using implementation "xts-aes-ce"

We've already found the similar message in fs/crypto/keyinfo.c to be very useful.

Signed-off-by Eric Biggers <[email protected]>

---
 drivers/md/dm-crypt.c | 9 +++++++++
 1 file changed, 9 insertions(+)

drivers/md/dm-crypt.c +9 -1

index b8eec515a003..7646135487be 100644
@@ -1885,6 +1885,13 @@ static int crypt_alloc_tfms_skcipher(struct crypt_config *cc, char *ciphermode)
                }
        }
 
+       /*
+        * dm-crypt performance can vary greatly depending on which crypto
+        * algorithm implementation is used.  Help people debug performance
+        * problems by logging the ->cra_driver_name.
+        */
+       DMINFO("%s using implementation \"%s\"", ciphermode,
+              crypto_skcipher_alg(any_tfm(cc))->base.cra_driver_name);
        return 0;
 }
 

@@ -1903,6 +1910,8 @@ static int crypt_alloc_tfms_aead(struct crypt_config *cc, char *ciphermode)
                return err;
        }
 
+       DMINFO("%s using implementation \"%s\"", ciphermode,
+              crypto_aead_alg(any_tfm_aead(cc))->base.cra_driver_name);
        return 0;
 }
 
--

2.19.2