crypto: qat - use pre-allocated buffers in datapath

crypto: qat - use pre-allocated buffers in datapath

In order to do DMAs, the QAT device requires that the scatterlist
structures are mapped and translated into a format that the firmware can
understand. This is defined as the composition of a scatter gather list
(SGL) descriptor header, the struct qat_alg_buf_list, plus a variable
number of flat buffer descriptors, the struct qat_alg_buf.

The allocation and mapping of these data structures is done each time a
request is received from the skcipher and aead APIs.
In an OOM situation, this behaviour might lead to a dead-lock if an
allocation fails.

Based on the conversation in [1], increase the size of the aead and
skcipher request contexts to include an SGL descriptor that can handle
a maximum of 4 flat buffers.
If requests exceed 4 entries buffers, memory is allocated dynamically.

[1] https://lore.kernel.org/linux-crypto/20200722072932.GA27544@gondor.apana.org.au/

Cc: stable@vger.kernel.org
Fixes: 469a759ea0f6 ("crypto: qat - Intel(R) QAT crypto interface")
Reported-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Reviewed-by: Marco Chiappero <marco.chiappero@intel.com>
Reviewed-by: Wojciech Ziemba <wojciech.ziemba@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>