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Message-ID: <013150d0-c2cd-847a-6e6d-3292035b208d@rivosinc.com>
Date: Fri, 4 Nov 2022 15:08:56 -0700
From: Vineet Gupta <vineetg@...osinc.com>
To: Chris Stillson <stillson@...osinc.com>
Cc: Greentime Hu <greentime.hu@...ive.com>,
Andrew Waterman <andrew@...ive.com>,
Nick Knight <nick.knight@...ive.com>,
Guo Ren <guoren@...ux.alibaba.com>,
Vincent Chen <vincent.chen@...ive.com>,
Ruinland Tsai <ruinland.tsai@...ive.com>,
kernel test robot <lkp@...el.com>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
Eric Biederman <ebiederm@...ssion.com>,
Kees Cook <keescook@...omium.org>,
Anup Patel <anup@...infault.org>,
Atish Patra <atishp@...shpatra.org>,
Oleg Nesterov <oleg@...hat.com>, Guo Ren <guoren@...nel.org>,
Heinrich Schuchardt <heinrich.schuchardt@...onical.com>,
Conor Dooley <conor.dooley@...rochip.com>,
linux-riscv <linux-riscv@...ts.infradead.org>,
lkml <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
Andy Chiu <andy.chiu@...ive.com>
Subject: Re: [PATCH v12 08/17] riscv: Add task switch support for vector
On 9/21/22 14:43, Chris Stillson wrote:
> From: Greentime Hu <greentime.hu@...ive.com>
>
> This patch adds task switch support for vector. It supports partial lazy
> save and restore mechanism. It also supports all lengths of vlen.
>
> [guoren@...ux.alibaba.com: First available porting to support vector
> context switching]
> [nick.knight@...ive.com: Rewrite vector.S to support dynamic vlen, xlen and
> code refine]
> [vincent.chen@...ive.com: Fix the might_sleep issue in vstate_save,
> vstate_restore]
> [andrew@...ive.com: Optimize task switch codes of vector]
> [ruinland.tsai@...ive.com: Fix the arch_release_task_struct free wrong
> datap issue]
>
> Suggested-by: Andrew Waterman <andrew@...ive.com>
> Co-developed-by: Nick Knight <nick.knight@...ive.com>
> Signed-off-by: Nick Knight <nick.knight@...ive.com>
> Co-developed-by: Guo Ren <guoren@...ux.alibaba.com>
> Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
> Co-developed-by: Vincent Chen <vincent.chen@...ive.com>
> Signed-off-by: Vincent Chen <vincent.chen@...ive.com>
> Co-developed-by: Ruinland Tsai <ruinland.tsai@...ive.com>
> Signed-off-by: Ruinland Tsai <ruinland.tsai@...ive.com>
> Signed-off-by: Greentime Hu <greentime.hu@...ive.com>
> Reported-by: kernel test robot <lkp@...el.com>
> Reported-by: kernel test robot <lkp@...el.com>
> ---
> arch/riscv/include/asm/switch_to.h | 66 ++++++++++++++++++++++++++++++
> arch/riscv/kernel/Makefile | 1 +
> arch/riscv/kernel/process.c | 43 +++++++++++++++++++
> 3 files changed, 110 insertions(+)
>
> diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
> index df1aa589b7fd..527951c033d4 100644
> --- a/arch/riscv/include/asm/switch_to.h
> +++ b/arch/riscv/include/asm/switch_to.h
> @@ -7,11 +7,13 @@
> #define _ASM_RISCV_SWITCH_TO_H
>
> #include <linux/jump_label.h>
> +#include <linux/slab.h>
> #include <linux/sched/task_stack.h>
> #include <asm/hwcap.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);
> @@ -68,6 +70,68 @@ static __always_inline bool has_fpu(void) { return false; }
> #define __switch_to_fpu(__prev, __next) do { } while (0)
> #endif
>
> +#ifdef CONFIG_VECTOR
> +extern struct static_key_false cpu_hwcap_vector;
> +static __always_inline bool has_vector(void)
> +{
> + return static_branch_likely(&cpu_hwcap_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);
> +
> + __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);
> +
> + __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
> +static __always_inline bool has_vector(void) { return false; }
> +#define riscv_vsize (0)
> +#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
All of this needs to be moved into vector.h for better containment.
I would also wire in struct __riscv_v_state vstate in struct
thread_struct in this patch.
> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> index 33bb60a354cd..35752fb6d145 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -55,6 +55,7 @@ obj-$(CONFIG_MMU) += vdso.o vdso/
>
> obj-$(CONFIG_RISCV_M_MODE) += traps_misaligned.o
> obj-$(CONFIG_FPU) += fpu.o
> +obj-$(CONFIG_VECTOR) += vector.o
This needs to go into last patch which adds Kconfig/Makefile enabling.
> +
> + if (has_vector()) {
Would it make sense to add IS_ENABLED(CONFIG_VECTOR) inside this helper
- would help compiler remove the codegen completely for !VECTOR but
still having some build test coverage. Anyhow this is minor point and
can be added later.
> + struct __riscv_v_state *vstate = &(current->thread.vstate);
> +
> + /* Enable vector and allocate memory for vector registers. */
> + if (!vstate->datap) {
> + vstate->datap = kzalloc(riscv_vsize, GFP_KERNEL);
> + if (WARN_ON(!vstate->datap))
> + return;
> + }
> + regs->status |= SR_VS_INITIAL;
> +
> + /*
> + * Restore the initial value to the vector register
> + * before starting the user program.
> + */
> + vstate_restore(current, regs);
> + }
> +
...
> +#ifdef CONFIG_VECTOR
> + /* Reset vector state */
> + vstate_off(current, task_pt_regs(current));
> + memset(¤t->thread.vstate, 0, RISCV_V_STATE_DATAP);
> +#endif
This doesn't check has_vector() as we want to unconditionally clean
memory for security reasons ?
> }
>
> int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
> {
> fstate_save(src, task_pt_regs(src));
> *dst = *src;
> + dst->thread.vstate.datap = NULL;
has_vector() needed here ?
>
> +void arch_release_task_struct(struct task_struct *tsk)
> +{
> + /* Free the vector context of datap. */
> + if (has_vector() && tsk->thread.vstate.datap)
> + kfree(tsk->thread.vstate.datap);
> +}
> +
> int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
> {
> unsigned long clone_flags = args->flags;
> @@ -175,7 +208,17 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
> p->thread.ra = (unsigned long)ret_from_kernel_thread;
> p->thread.s[0] = (unsigned long)args->fn;
> p->thread.s[1] = (unsigned long)args->fn_arg;
> + p->thread.vstate.datap = NULL;
> } else {
> + /* Allocate the datap for the user process if datap is NULL */
> + if (has_vector() && !p->thread.vstate.datap) {
> + void *datap = kzalloc(riscv_vsize, GFP_KERNEL);
> + /* Failed to allocate memory. */
> + if (!datap)
> + return -ENOMEM;
> + p->thread.vstate.datap = datap;
> + memset(&p->thread.vstate, 0, RISCV_V_STATE_DATAP);
> + }
> *childregs = *(current_pt_regs());
> if (usp) /* User fork */
> childregs->sp = usp;
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