Re: [PATCH v8 4/8] crypto: caam - simplify RNG implementation

[Horia GeantÄ]

On 3/16/2020 5:01 PM, Andrey Smirnov wrote:
> Rework CAAM RNG implementation as follows:
> 
> - Make use of the fact that HWRNG supports partial reads and will
> handle such cases gracefully by removing recursion in caam_read()
> 
> - Convert blocking caam_read() codepath to do a single blocking job
> read directly into requested buffer, bypassing any intermediary
> buffers
> 
> - Convert async caam_read() codepath into a simple single
> reader/single writer FIFO use-case, thus simplifying concurrency
> handling and delegating buffer read/write position management to KFIFO
> subsystem.
> 
> - Leverage the same low level RNG data extraction code for both async
> and blocking caam_read() scenarios, get rid of the shared job
> descriptor and make non-shared one as a simple as possible (just
> HEADER + ALGORITHM OPERATION + FIFO STORE)
> 
> - Split private context from DMA related memory, so that the former
> could be allocated without GFP_DMA.
> 
> NOTE: On its face value this commit decreased throughput numbers
> reported by
> 
>   dd if=/dev/hwrng of=/dev/null bs=1 count=100K [iflag=nonblock]
> 
> by about 15%, however commits that enable prediction resistance and
> limit JR total size impact the performance so much and move the
> bottleneck such as to make this regression irrelevant.
> 
> NOTE: On the bright side, this commit reduces RNG in kernel DMA buffer
> memory usage from 2 x RN_BUF_SIZE (~256K) to 32K.
> 
> Signed-off-by: Andrey Smirnov <andrew.smirnov@xxxxxxxxx>
> Cc: Chris Healy <cphealy@xxxxxxxxx>
> Cc: Lucas Stach <l.stach@xxxxxxxxxxxxxx>
> Cc: Horia GeantÄ <horia.geanta@xxxxxxx>
> Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
> Cc: Iuliana Prodan <iuliana.prodan@xxxxxxx>
> Cc: linux-crypto@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: linux-imx@xxxxxxx
Reviewed-by: Horia GeantÄ <horia.geanta@xxxxxxx>

Thanks,
Horia