After commit f5ff79fd ("dma-mapping: remove CONFIG_DMA_REMAP"), if
the algorithms are enabled, the driver crashes with a BUG_ON while
executing vunmap() in the context of a tasklet. This is due to the fact
that the function dma_free_coherent() cannot be called in an interrupt
context (see Documentation/core-api/dma-api-howto.rst).

The functions qat_rsa_enc() and qat_rsa_dec() allocate memory with
dma_alloc_coherent() if the source or the destination buffers are made
of multiple flat buffers or of a size that is not compatible with the
hardware.
This memory is then freed with dma_free_coherent() in the context of a
tasklet invoked to handle the response for the corresponding request.

Replace allocations with dma_alloc_coherent() in the functions
qat_rsa_enc() and qat_rsa_dec() with kmalloc() + dma_map_single().

Cc: stable@vger.kernel.org
Fixes: a9905320 ("crypto: qat - Add support for RSA algorithm")
Signed-off-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Reviewed-by: Adam Guerin <adam.guerin@intel.com>
Reviewed-by: Wojciech Ziemba <wojciech.ziemba@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>