Re: [PATCH 12/12] RISC-V: crypto: add Zvkb accelerated ChaCha20 implementation

[Jerry Shih]

On Nov 23, 2023, at 02:20, Conor Dooley <conor@xxxxxxxxxx> wrote:
> On Thu, Nov 23, 2023 at 01:37:33AM +0800, Jerry Shih wrote:
>> On Nov 21, 2023, at 21:14, Conor Dooley <conor.dooley@xxxxxxxxxxxxx> wrote:
>>> On Tue, Nov 21, 2023 at 06:55:07PM +0800, Jerry Shih wrote:
>>>> Sorry, I just use my `internal` qemu with vector-crypto and rva22 patches.
>>>> 
>>>> The public qemu haven't supported rva22 profiles. Here is the qemu patch[1] for
>>>> that. But here is the discussion why the qemu doesn't export these
>>>> `named extensions`(e.g. Zicclsm).
>>>> I try to add Zicclsm in DT in the v2 patch set. Maybe we will have more discussion
>>>> about the rva22 profiles in kernel DT.
>>> 
>>> Please do, that'll be fun! Please take some time to read what the
>>> profiles spec actually defines Zicclsm fore before you send those patches
>>> though. I think you might come to find you have misunderstood what it
>>> means - certainly I did the first time I saw it!
>> 
>> From the rva22 profile:
> 
> "rva22" is not a profile. As I pointed out to Eric, this is defined in
> the RVA22U64 profile (and the RVA20U64 one, but that is effectively a
> moot point). The profile descriptions for these only specify "the ISA
> features available to user-mode execution environments", so it is not
> suitable for use in any other context.

I missed that important part: it's for user space.
Thx.

>>  This requires misaligned support for all regular load and store instructions (including
>>  scalar and ``vector``)
>> 
>> The spec includes the explicit `vector` keyword.
>> So, I still think we could use Zicclsm checking for these vector-crypto implementations.
> 
> In userspace, if Zicclsm was exported somewhere, that would be a valid
> argument. Even for userspace, the hwprobe flags probably provide more
> information though, since the firmware emulation is insanely slow.

I agree. It will be more useful to have the flag like `VECTOR_MISALIGNED_FAST`
instead.

>> My proposed patch is just a simple patch which only update the DT document and
>> update the isa string parser for Zicclsm.
> 
> Zicclsm has no meaning outside of user mode, so it's not suitable for
> use in that context. Other "features" defined in the profiles spec might
> be suitable for inclusion, but it'll be a case-by-case basis.

I will skip the Zicclsm part in my v2 patch.

>> If it's still not recommend to use Zicclsm
>> checking, I will turn to use `RISCV_HWPROBE_MISALIGNED_*` instead.
> 
> Palmer has commented on the rest, so no need for me :)

All crypto algorithms will assume that the vector supports misaligned access in next
v2 patch.
And the algorithms will also not check for `RISCV_HWPROBE_MISALIGNED_*` since
it's related to scalar accesses.
Once we have the vector performance related flag, we could go back here to use it.

-Jerry