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

[Jerry Shih]

On Nov 21, 2023, at 03:18, Eric Biggers <ebiggers@xxxxxxxxxx> wrote:
> First, I can see your updated patchset at branch
> "dev/jerrys/vector-crypto-upstream-v2" of https://github.com/JerryShih/linux,
> but I haven't seen it on the mailing list yet.  Are you planning to send it out?

I will send it out soon.

> Second, with your updated patchset, I'm not seeing any of the RISC-V optimized
> algorithms be registered when I boot the kernel in QEMU.  This is caused by the
> new check 'riscv_isa_extension_available(NULL, ZICCLSM)' not passing.  Is
> checking for "Zicclsm" the correct way to determine whether unaligned memory
> accesses are supported?
> 
> I'm using 'qemu-system-riscv64 -cpu max -machine virt', with the very latest
> QEMU commit (af9264da80073435), so it should have all the CPU features.
> 
> - Eric

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.

[1]
LINK: https://lore.kernel.org/all/d1d6f2dc-55b2-4dce-a48a-4afbbf6df526@xxxxxxxxxxxxxxxx/#t

I don't know whether it's a good practice to check unaligned access using
`Zicclsm`. 

Here is another related cpu feature for unaligned access:
RISCV_HWPROBE_MISALIGNED_*
But it looks like it always be initialized with `RISCV_HWPROBE_MISALIGNED_SLOW`[2].
It implies that linux kernel always supports unaligned access. But we have the
actual HW which doesn't support unaligned access for vector unit.

[2]
LINK: https://github.com/torvalds/linux/blob/98b1cc82c4affc16f5598d4fa14b1858671b2263/arch/riscv/kernel/cpufeature.c#L575

I will still use `Zicclsm` checking in this stage for reviewing. And I will create qemu
branch with Zicclsm enabled feature for testing.

-Jerry