[PATCH 06/12] RISC-V: crypto: add accelerated AES-CBC/CTR/ECB/XTS implementations

[Jerry Shih]

On Nov 9, 2023, at 15:16, Eric Biggers <ebiggers at kernel.org> wrote:
> On Tue, Nov 07, 2023 at 04:53:13PM +0800, Jerry Shih wrote:
>> On Nov 2, 2023, at 13:16, Eric Biggers <ebiggers at kernel.org> wrote:
>>> On Thu, Oct 26, 2023 at 02:36:38AM +0800, Jerry Shih wrote:
>>>> +static int ecb_encrypt(struct skcipher_request *req)
>>>> +{
>>> 
>>> There's no fallback for !crypto_simd_usable() here.  I really like it this way.
>>> However, for it to work (for skciphers and aeads), RISC-V needs to allow the
>>> vector registers to be used in softirq context.  Is that already the case?
>> 
>> The kernel-mode-vector could be enabled in softirq, but we don't have nesting
>> vector contexts. Will we have the case that kernel needs to jump to softirq for
>> encryptions during the regular crypto function? If yes, we need to have fallbacks
>> for all algorithms.
> 
> Are you asking what happens if a softirq is taken while the CPU is between
> kernel_vector_begin() and kernel_vector_end()?  I think that needs to be
> prevented by making kernel_vector_begin() and kernel_vector_end() disable and
> re-enable softirqs, like what kernel_neon_begin() and kernel_neon_end() do on
> arm64.  Refer to commit 13150149aa6ded which implemented that behavior on arm64.
> 
> - Eric

The current kernel-mode-vector implementation, it only calls `preempt_disable()` during
vector context. So, we will hit nesting vector context issue from softirq which also use
kernel-vector.
https://lore.kernel.org/all/20230721112855.1006-1-andy.chiu@sifive.com/

Maybe we could use the `simd_register_aeads_compat()` wrapping as x86 platform
first in a simpler way first.

-Jerry