linux-kernel - Re: [PATCH v9 08/17] riscv: Add vector struct and assembler definitions

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Message-ID: <mhng-a7a94a37-5791-4c76-8f2d-072130d71819@palmer-ri-x1c9>
Date:   Tue, 14 Dec 2021 08:29:30 -0800 (PST)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     greentime.hu@...ive.com
CC:     Paul Walmsley <paul.walmsley@...ive.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        aou@...s.berkeley.edu
Subject:     Re: [PATCH v9 08/17] riscv: Add vector struct and assembler definitions

On Tue, 09 Nov 2021 01:48:20 PST (-0800), greentime.hu@...ive.com wrote:
> Add vector state context struct in struct thread and asm-offsets.c
> definitions.
>
> The vector registers will be saved in datap pointer of __riscv_v_state. It
> will be dynamically allocated in kernel space. It will be put right after
> the __riscv_v_state data structure in user space.
>
> Co-developed-by: Vincent Chen <vincent.chen@...ive.com>
> Signed-off-by: Vincent Chen <vincent.chen@...ive.com>
> Signed-off-by: Greentime Hu <greentime.hu@...ive.com>
> ---
>  arch/riscv/include/asm/processor.h   |  1 +
>  arch/riscv/include/uapi/asm/ptrace.h | 11 +++++++++++
>  arch/riscv/kernel/asm-offsets.c      |  6 ++++++
>  3 files changed, 18 insertions(+)
>
> diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
> index 46b492c78cbb..a268f1382e52 100644
> --- a/arch/riscv/include/asm/processor.h
> +++ b/arch/riscv/include/asm/processor.h
> @@ -35,6 +35,7 @@ struct thread_struct {
>  	unsigned long s[12];	/* s[0]: frame pointer */
>  	struct __riscv_d_ext_state fstate;
>  	unsigned long bad_cause;
> +	struct __riscv_v_state vstate;
>  };
>
>  /* Whitelist the fstate from the task_struct for hardened usercopy */
> diff --git a/arch/riscv/include/uapi/asm/ptrace.h b/arch/riscv/include/uapi/asm/ptrace.h
> index 882547f6bd5c..bd3b8a710246 100644
> --- a/arch/riscv/include/uapi/asm/ptrace.h
> +++ b/arch/riscv/include/uapi/asm/ptrace.h
> @@ -77,6 +77,17 @@ union __riscv_fp_state {
>  	struct __riscv_q_ext_state q;
>  };
>
> +struct __riscv_v_state {
> +	unsigned long vstart;
> +	unsigned long vl;
> +	unsigned long vtype;
> +	unsigned long vcsr;

Don't we also need vlen to adequately determine the vector state?  
Otherwise we're going to end up dropping some state when vl isn't vlmax, 
which IIUC isn't legal.

> +	void *datap;
> +#if __riscv_xlen == 32
> +	__u32 __padding;
> +#endif

Why is there padding?

> +};
> +
>  #endif /* __ASSEMBLY__ */
>
>  #endif /* _UAPI_ASM_RISCV_PTRACE_H */
> diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c
> index 90f8ce64fa6f..34f43c84723a 100644
> --- a/arch/riscv/kernel/asm-offsets.c
> +++ b/arch/riscv/kernel/asm-offsets.c
> @@ -72,6 +72,12 @@ void asm_offsets(void)
>  	OFFSET(TSK_STACK_CANARY, task_struct, stack_canary);
>  #endif
>
> +	OFFSET(RISCV_V_STATE_VSTART, __riscv_v_state, vstart);
> +	OFFSET(RISCV_V_STATE_VL, __riscv_v_state, vl);
> +	OFFSET(RISCV_V_STATE_VTYPE, __riscv_v_state, vtype);
> +	OFFSET(RISCV_V_STATE_VCSR, __riscv_v_state, vcsr);
> +	OFFSET(RISCV_V_STATE_DATAP, __riscv_v_state, datap);
> +
>  	DEFINE(PT_SIZE, sizeof(struct pt_regs));
>  	OFFSET(PT_EPC, pt_regs, epc);
>  	OFFSET(PT_RA, pt_regs, ra);