[dm-devel] [PATCH v3] dm: switch dm-verity to async hash crypto API

[Milan Broz]

On 02/19/2017 01:46 PM, Gilad Ben-Yossef wrote:
> Use of the synchronous digest API limits dm-verity to using pure
> CPU based algorithm providers and rules out the use of off CPU
> algorithm providers which are normally asynchronous by nature,
> potentially freeing CPU cycles.
> 
> This can reduce performance per Watt in situations such as during
> boot time when a lot of concurrent file accesses are made to the
> protected volume.
> 
> Move DM_VERITY to the asynchronous hash API.
> 
> Signed-off-by: Gilad Ben-Yossef <gilad at benyossef.com>
> CC: Eric Biggers <ebiggers3 at gmail.com>
> CC: Ondrej Mosnáček <omosnacek+linux-crypto at gmail.com>
> CC: Milan Broz <gmazyland at gmail.com>
> ---
> 
> The patch was tested on an Armv7 based dual core Zynq ZC706 development
> board with SHA256-asm, SHA256-neon synchronous providers with no visible
> degradation of performance, with cryptd based asynchronous versions of the 
> same and with an off tree Arm CryptoCell asynchronous provider.
> 
> Changes from v2:
> 
> - Use completion to potentially wait also on crypto_ahash_init() as it
>   may finish asynchronously as well in some drivers, such as cryptd, as
>   discovered by Milan Broz.

This version survived my simple veritysetup test (in cryptsetup package)
with forced async path so I think it is ok for 4.12 queue...

Thanks,
Milan


> - Use sg_init_one() where apropriate as pointed out by Milan Broz.
> 
> Changes from v1:
> 
> - Use a 0 mask to allocate crypto alg indicating we welcome async algo 
>   providers, as suggested by Ondrej Mosnáček.
> - Fix use of un-initialized completion when using async provider for IO
>   blocks hashing
> - Pass flag indicating we are OK with crypto provider backlog
> - Re-factor checking for need to wait into a common function
>