Re: [PATCH 0/7] crypto: switch to static calls for CRC-T10DIF
flat view
From: Ard Biesheuvel <ardb@kernel.org>
Date: 2021-01-11 17:29:05
On Mon, 11 Jan 2021 at 17:52, Ard Biesheuvel [off-list ref] wrote:
CRC-T10DIF is a very poor match for the crypto API: - every user in the kernel calls it via a library wrapper around the shash API, so all callers share a single instance of the transform - each architecture provides at most a single optimized implementation, based on SIMD instructions for carryless multiplication In other words, none of the flexibility it provides is put to good use, and so it is better to get rid of this complexity, and expose the optimized implementations via static calls instead. This removes a substantial chunk of code, and also gets rid of any indirect calls on architectures that obsess about those (x86) If this approach is deemed suitable, there are other places where we might consider adopting it: CRC32 and CRC32(C). Patch #1 does some preparatory refactoring and removes the library wrapper around the shash transform. Patch #2 introduces the actual static calls, along with the registration routines to update the crc-t10dif implementation at runtime. Patch #3 updates the generic CRC-T10DIF shash driver so it distinguishes between the optimized library code and the generic library code. Patches #4 to #7 update the various arch implementations to switch over to the new method. Special request to Peter to take a look at patch #2, and in particular, whether synchronize_rcu_tasks() is sufficient to ensure that a module providing the target of a static call can be unloaded safely.
It seems I may have managed to confuse myself slightly here: without an upper bound on the size of the input of the crc_t10dif() routine, I suppose we can never assume that all its callers have finished. Insights welcome ...