Re: [PATCH -next v18 00/20] riscv: Add vector ISA support

Andy Chiu
2023-04-17T16:26:55Z

Hi Ben,

On Mon, Apr 17, 2023 at 11:56 PM Ben Dooks <ben.dooks@codethink.co.uk> wrote:
>
> On 14/04/2023 16:58, Andy Chiu wrote:
> > This patchset is implemented based on vector 1.0 spec to add vector support
> > in riscv Linux kernel. There are some assumptions for this implementations.
> >
> > 1. We assume all harts has the same ISA in the system.
> > 2. We disable vector in both kernel and user space [1] by default. Only
> > enable an user's vector after an illegal instruction trap where it
> > actually starts executing vector (the first-use trap [2]).
> > 3. We detect "riscv,isa" to determine whether vector is support or not.
> >
> > We defined a new structure __riscv_v_ext_state in struct thread_struct to
> > save/restore the vector related registers. It is used for both kernel space
> > and user space.
> > - In kernel space, the datap pointer in __riscv_v_ext_state will be
> > allocated to save vector registers.
> > - In user space,
> > - In signal handler of user space, the structure is placed
> > right after __riscv_ctx_hdr, which is embedded in fp reserved
> > aera. This is required to avoid ABI break [2]. And datap points
> > to the end of __riscv_v_ext_state.
> > - In ptrace, the data will be put in ubuf in which we use
> > riscv_vr_get()/riscv_vr_set() to get or set the
> > __riscv_v_ext_state data structure from/to it, datap pointer
> > would be zeroed and vector registers will be copied to the
> > address right after the __riscv_v_ext_state structure in ubuf.
> >
> > This patchset is rebased to v6.3-rc1 and it is tested by running several
> > vector programs simultaneously. It delivers signals correctly in a test
> > where we can see a valid ucontext_t in a signal handler, and a correct V
> > context returing back from it. And the ptrace interface is tested by
> > PTRACE_{GET,SET}REGSET. Lastly, KVM is tested by running above tests in
> > a guest using the same kernel image. All tests are done on an rv64gcv
> > virt QEMU.
>
> Ok, are there plans for in-kernel vector patches, or have I missed
> something in this list? I expect once things like the vector-crypto
> hit then people will be wanting in-kernel accelerators.
>

Yes, I am redesigning and planning to submit the in-kernel Vector
support recently. Currently the original one is carried by Heiko's
vector crypto series. The API interface of the refined one should
remain the same but with some optimizations.

> --
> Ben Dooks http://www.codethink.co.uk/
> Senior Engineer Codethink - Providing Genius
>
> https://www.codethink.co.uk/privacy.html
>

Cheers,
Andy