[RFC PATCH] crypto: riscv: scalar accelerated GHASH

[Qingfang Deng]

Hi Eric,

On Fri, Apr 18, 2025 at 12:59 AM Eric Biggers <ebiggers at kernel.org> wrote:
>
> On Thu, Apr 17, 2025 at 04:42:46PM +0800, Qingfang Deng wrote:
> > > I see. But do you have a particular configuration in mind? Does it
> > > have scalar AES too? I looked into that a while ago but I was told
> > > that nobody actually incorporates that. So what about these
> > > extensions? Are they commonly implemented?
> >
> > It's aes-generic.c (LUT-based) with accelerated GHASH.
>
> That's an odd combination.  Normally accelerated AES and GHASH go together.
> Presumably you're targeting some specific RISC-V CPU.  Is this going to be a
> one-off thing for that specific CPU?  Or can we expect many RISC-V CPUs to have
> GHASH acceleration without AES?  And if so, why?

There are a few RISC-V CPUs that support the B extensions
(Zba+Zbb+Zbc+Zbs) but lack both scalar and vector crypto extensions.
One such CPU already upstreamed in the kernel is the SpacemiT K1.
Another example and the one I'm currently running this code on is the
XuanTie C908, as found in the CanMV K230.

(+Cc Guo Ren)
Guo, do you know if future XuanTie CPUs will support the RISC-V
scalar/vector crypto extensions?

[1] https://www.xrvm.com/product/xuantie/C908
[2] https://www.xrvm.com/product/xuantie/C907
[3] https://docs.banana-pi.org/en/BPI-F3/SpacemiT_K1_datasheet
>
> - Eric