Re: [RFC PATCH v4 10/13] riscv: Add task switch support for vector

From: Guo Ren
Date: Sun May 31 2020 - 11:37:12 EST

Hi Greentime,

On Tue, May 26, 2020 at 3:03 PM Greentime Hu <greentime.hu@xxxxxxxxxx> wrote:
>
> From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
>
> This patch adds task switch support for vector. It supports lazy
> save and restore mechanism. It also supports all lengths of vlen.
>
> [greentime.hu@xxxxxxxxxx: add support for dynamic vlen, fix
> __vstate_clean() and lazy save/restore bug]
> [nick.knight@xxxxxxxxxx: Rewrite vector.S to support dynamic vlen, xlen and
> code refine]
> Signed-off-by: Nick Knight <nick.knight@xxxxxxxxxx>
> Signed-off-by: Greentime Hu <greentime.hu@xxxxxxxxxx>
> Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> ---
> arch/riscv/include/asm/switch_to.h | 71 +++++++++++++++++++++++++
> arch/riscv/kernel/Makefile | 1 +
> arch/riscv/kernel/process.c | 40 ++++++++++++++
> arch/riscv/kernel/vector.S | 84 ++++++++++++++++++++++++++++++
> 4 files changed, 196 insertions(+)
> create mode 100644 arch/riscv/kernel/vector.S
>
> diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
> index b9234e7178d0..a047dd75e09d 100644
> --- a/arch/riscv/include/asm/switch_to.h
> +++ b/arch/riscv/include/asm/switch_to.h
> @@ -6,10 +6,12 @@
> #ifndef _ASM_RISCV_SWITCH_TO_H
> #define _ASM_RISCV_SWITCH_TO_H
>
> +#include <linux/slab.h>
> #include <linux/sched/task_stack.h>
> #include <asm/processor.h>
> #include <asm/ptrace.h>
> #include <asm/csr.h>
> +#include <asm/asm-offsets.h>
>
> #ifdef CONFIG_FPU
> extern void __fstate_save(struct task_struct *save_to);
> @@ -63,6 +65,73 @@ extern bool has_fpu;
> #define __switch_to_fpu(__prev, __next) do { } while (0)
> #endif
>
> +#ifdef CONFIG_VECTOR
> +extern bool has_vector;
> +extern unsigned long riscv_vsize;
> +extern void __vstate_save(struct __riscv_v_state *save_to, void *datap);
> +extern void __vstate_restore(struct __riscv_v_state *restore_from, void *datap);
> +
> +static inline void __vstate_clean(struct pt_regs *regs)
> +{
> + regs->status = (regs->status & ~(SR_VS)) | SR_VS_CLEAN;
> +}
> +
> +static inline void vstate_off(struct task_struct *task,
> + struct pt_regs *regs)
> +{
> + regs->status = (regs->status & ~SR_VS) | SR_VS_OFF;
> +}
> +
> +static inline void vstate_save(struct task_struct *task,
> + struct pt_regs *regs)
> +{
> + if ((regs->status & SR_VS) == SR_VS_DIRTY) {
> + struct __riscv_v_state *vstate = &(task->thread.vstate);
> +
> + /* Allocate space for vector registers. */
> + if (!vstate->datap) {
> + vstate->datap = kzalloc(riscv_vsize, GFP_KERNEL);
> + vstate->size = riscv_vsize;
> + }
> + __vstate_save(vstate, vstate->datap);
> + __vstate_clean(regs);
> + }
> +}
> +
> +static inline void vstate_restore(struct task_struct *task,
> + struct pt_regs *regs)
> +{
> + if ((regs->status & SR_VS) != SR_VS_OFF) {
> + struct __riscv_v_state *vstate = &(task->thread.vstate);
> +
> + /* Allocate space for vector registers. */
> + if (!vstate->datap) {
> + vstate->datap = kzalloc(riscv_vsize, GFP_KERNEL);
> + vstate->size = riscv_vsize;
> + }
> + __vstate_restore(vstate, vstate->datap);
> + __vstate_clean(regs);
> + }
> +}
> +
> +static inline void __switch_to_vector(struct task_struct *prev,
> + struct task_struct *next)
> +{
> + struct pt_regs *regs;
> +
> + regs = task_pt_regs(prev);
> + if (unlikely(regs->status & SR_SD))
> + vstate_save(prev, regs);
> + vstate_restore(next, task_pt_regs(next));
> +}
> +
> +#else
> +#define has_vector false
> +#define vstate_save(task, regs) do { } while (0)
> +#define vstate_restore(task, regs) do { } while (0)
> +#define __switch_to_vector(__prev, __next) do { } while (0)
> +#endif
> +
> extern struct task_struct *__switch_to(struct task_struct *,
> struct task_struct *);
>
> @@ -72,6 +141,8 @@ do { \
> struct task_struct *__next = (next); \
> if (has_fpu) \
> __switch_to_fpu(__prev, __next); \
> + if (has_vector) \
> + __switch_to_vector(__prev, __next); \
> ((last) = __switch_to(__prev, __next)); \
> } while (0)
>
> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> index 86c83081044f..dee489a1a526 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -33,6 +33,7 @@ obj-$(CONFIG_MMU) += vdso.o vdso/
>
> obj-$(CONFIG_RISCV_M_MODE) += clint.o traps_misaligned.o
> obj-$(CONFIG_FPU) += fpu.o
> +obj-$(CONFIG_VECTOR) += vector.o
> obj-$(CONFIG_SMP) += smpboot.o
> obj-$(CONFIG_SMP) += smp.o
> obj-$(CONFIG_SMP) += cpu_ops.o
> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> index 610c11e91606..fc8761c04e9f 100644
> --- a/arch/riscv/kernel/process.c
> +++ b/arch/riscv/kernel/process.c
> @@ -76,6 +76,16 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
> */
> fstate_restore(current, regs);
> }
> +
> + if (has_vector) {
> + regs->status |= SR_VS_INITIAL;
> + /*
> + * Restore the initial value to the vector register
> + * before starting the user program.
> + */
> + vstate_restore(current, regs);
> + }
> +
> regs->epc = pc;
> regs->sp = sp;
> set_fs(USER_DS);
> @@ -92,15 +102,45 @@ void flush_thread(void)
> fstate_off(current, task_pt_regs(current));
> memset(&current->thread.fstate, 0, sizeof(current->thread.fstate));
> #endif
> +#ifdef CONFIG_VECTOR
> + /* Reset vector state */
> + vstate_off(current, task_pt_regs(current));
> + memset(&current->thread.vstate, 0, sizeof(current->thread.vstate));
> +#endif
> }
>
> int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
> {
> fstate_save(src, task_pt_regs(src));
> + if (has_vector)
> + /* To make sure every dirty vector context is saved. */
> + vstate_save(src, task_pt_regs(src));
> *dst = *src;
> + if (has_vector) {
> + /* Copy vector context to the forked task from parent. */
> + if ((task_pt_regs(src)->status & SR_VS) != SR_VS_OFF) {
Is this necessary, I mean in start_thread() we force SR_VS_INITIAL
when has_vector = 1.

Maybe you want to distinguish different processes with/without vector?


> + unsigned long size = src->thread.vstate.size;
> +
> + dst->thread.vstate.datap = kzalloc(size, GFP_KERNEL);
> + /* Failed to allocate memory. */
> + if (!dst->thread.vstate.datap)
> + return -ENOMEM;
> + /* Copy the src vector context to dst. */
> + memcpy(dst->thread.vstate.datap,
> + src->thread.vstate.datap, size);
> + }
> + }
> +
> return 0;
> }
>
> +void arch_release_task_struct(struct task_struct *tsk)
> +{
> + /* Free the vector context of datap. */
> + if (has_vector)
> + kfree(tsk->thread.vstate.datap);
> +}
> +
> int copy_thread_tls(unsigned long clone_flags, unsigned long usp,
> unsigned long arg, struct task_struct *p, unsigned long tls)
> {
> diff --git a/arch/riscv/kernel/vector.S b/arch/riscv/kernel/vector.S
> new file mode 100644
> index 000000000000..91d5dd29cd0f
> --- /dev/null
> +++ b/arch/riscv/kernel/vector.S
> @@ -0,0 +1,84 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2012 Regents of the University of California
> + * Copyright (C) 2017 SiFive
> + * Copyright (C) 2019 Alibaba Group Holding Limited
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation, version 2.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + */
> +
> +#include <linux/linkage.h>
> +
> +#include <asm/asm.h>
> +#include <asm/csr.h>
> +#include <asm/asm-offsets.h>
> +
> +#define vstatep a0
> +#define datap a1
> +#define x_vstart t0
> +#define x_vtype t1
> +#define x_vl t2
> +#define x_vcsr t3
> +#define incr t4
> +#define m_one t5
> +#define status t6
> +
> +ENTRY(__vstate_save)
> + li status, SR_VS
> + csrs sstatus, status
> +
> + csrr x_vstart, CSR_VSTART
> + csrr x_vtype, CSR_VTYPE
> + csrr x_vl, CSR_VL
> + csrr x_vcsr, CSR_VCSR
> + li m_one, -1
> + vsetvli incr, m_one, e8, m8
> + vse.v v0, (datap)
> + add datap, datap, incr
> + vse.v v8, (datap)
> + add datap, datap, incr
> + vse.v v16, (datap)
> + add datap, datap, incr
> + vse.v v24, (datap)
> +
> + REG_S x_vstart, RISCV_V_STATE_VSTART(vstatep)
> + REG_S x_vtype, RISCV_V_STATE_VTYPE(vstatep)
> + REG_S x_vl, RISCV_V_STATE_VL(vstatep)
> + REG_S x_vcsr, RISCV_V_STATE_VCSR(vstatep)
> +
> + csrc sstatus, status
> + ret
> +ENDPROC(__vstate_save)
> +
> +ENTRY(__vstate_restore)
> + li status, SR_VS
> + csrs sstatus, status
> +
> + li m_one, -1
> + vsetvli incr, m_one, e8, m8
> + vle.v v0, (datap)
> + add datap, datap, incr
> + vle.v v8, (datap)
> + add datap, datap, incr
> + vle.v v16, (datap)
> + add datap, datap, incr
> + vle.v v24, (datap)
> +
> + REG_L x_vstart, RISCV_V_STATE_VSTART(vstatep)
> + REG_L x_vtype, RISCV_V_STATE_VTYPE(vstatep)
> + REG_L x_vl, RISCV_V_STATE_VL(vstatep)
> + REG_L x_vcsr, RISCV_V_STATE_VCSR(vstatep)
> + vsetvl x0, x_vl, x_vtype
> + csrw CSR_VSTART, x_vstart
> + csrw CSR_VCSR, x_vcsr
> +
> + csrc sstatus, status
> + ret
> +ENDPROC(__vstate_restore)
> --
> 2.26.2
>
>


--
Best Regards
Guo Ren

ML: https://lore.kernel.org/linux-csky/