Re: [PATCH v3 2/6] riscv: Deduplicate IRQ stack switching

Guo Ren
2023-08-29T03:35:42Z

On Tue, Aug 29, 2023 at 3:58 AM Sami Tolvanen <samitolvanen@google.com> wrote:
>
> With CONFIG_IRQ_STACKS, we switch to a separate per-CPU IRQ stack
> before calling handle_riscv_irq or __do_softirq. We currently
> have duplicate inline assembly snippets for stack switching in
> both code paths. Now that we can access per-CPU variables in
> assembly, implement call_on_irq_stack in assembly, and use that
> instead of redudant inline assembly.
>
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> Tested-by: Nathan Chancellor <nathan@kernel.org>
> ---
> arch/riscv/include/asm/asm.h | 5 +++++
> arch/riscv/include/asm/irq_stack.h | 3 +++
> arch/riscv/kernel/asm-offsets.c | 5 +++++
> arch/riscv/kernel/entry.S | 30 +++++++++++++++++++++++++
> arch/riscv/kernel/irq.c | 35 +++++++-----------------------
> arch/riscv/kernel/traps.c | 32 ++++-----------------------
> 6 files changed, 55 insertions(+), 55 deletions(-)
>
> diff --git a/arch/riscv/include/asm/asm.h b/arch/riscv/include/asm/asm.h
> index bfb4c26f113c..8e446be2d57c 100644
> --- a/arch/riscv/include/asm/asm.h
> +++ b/arch/riscv/include/asm/asm.h
> @@ -104,6 +104,11 @@
> .endm
> #endif /* CONFIG_SMP */
>
> +.macro load_per_cpu dst ptr tmp
> + asm_per_cpu \dst \ptr \tmp
> + REG_L \dst, 0(\dst)
> +.endm
> +
> /* save all GPs except x1 ~ x5 */
> .macro save_from_x6_to_x31
> REG_S x6, PT_T1(sp)
> diff --git a/arch/riscv/include/asm/irq_stack.h b/arch/riscv/include/asm/irq_stack.h
> index e4042d297580..6441ded3b0cf 100644
> --- a/arch/riscv/include/asm/irq_stack.h
> +++ b/arch/riscv/include/asm/irq_stack.h
> @@ -12,6 +12,9 @@
>
> DECLARE_PER_CPU(ulong *, irq_stack_ptr);
>
> +asmlinkage void call_on_irq_stack(struct pt_regs *regs,
> + void (*func)(struct pt_regs *));
> +
> #ifdef CONFIG_VMAP_STACK
> /*
> * To ensure that VMAP'd stack overflow detection works correctly, all VMAP'd
> diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c
> index 9f535d5de33f..0af8860f9d68 100644
> --- a/arch/riscv/kernel/asm-offsets.c
> +++ b/arch/riscv/kernel/asm-offsets.c
> @@ -14,6 +14,7 @@
> #include <asm/thread_info.h>
> #include <asm/ptrace.h>
> #include <asm/cpu_ops_sbi.h>
> +#include <asm/stacktrace.h>
> #include <asm/suspend.h>
>
> void asm_offsets(void);
> @@ -480,4 +481,8 @@ void asm_offsets(void)
> OFFSET(KERNEL_MAP_VIRT_ADDR, kernel_mapping, virt_addr);
> OFFSET(SBI_HART_BOOT_TASK_PTR_OFFSET, sbi_hart_boot_data, task_ptr);
> OFFSET(SBI_HART_BOOT_STACK_PTR_OFFSET, sbi_hart_boot_data, stack_ptr);
> +
> + DEFINE(STACKFRAME_SIZE_ON_STACK, ALIGN(sizeof(struct stackframe), STACK_ALIGN));
> + OFFSET(STACKFRAME_FP, stackframe, fp);
> + OFFSET(STACKFRAME_RA, stackframe, ra);
> }
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index 3d11aa3af105..a306562636e4 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -218,6 +218,36 @@ SYM_CODE_START(ret_from_fork)
> tail syscall_exit_to_user_mode
> SYM_CODE_END(ret_from_fork)
>
> +#ifdef CONFIG_IRQ_STACKS
> +/*
> + * void call_on_irq_stack(struct pt_regs *regs,
> + * void (*func)(struct pt_regs *));
> + *
> + * Calls func(regs) using the per-CPU IRQ stack.
> + */
> +SYM_FUNC_START(call_on_irq_stack)
> + /* Create a frame record to save ra and s0 (fp) */
> + addi sp, sp, -STACKFRAME_SIZE_ON_STACK
> + REG_S ra, STACKFRAME_RA(sp)
> + REG_S s0, STACKFRAME_FP(sp)
> + addi s0, sp, STACKFRAME_SIZE_ON_STACK
> +
> + /* Switch to the per-CPU IRQ stack and call the handler */
> + load_per_cpu t0, irq_stack_ptr, t1
> + li t1, IRQ_STACK_SIZE
> + add sp, t0, t1
> + jalr a1
> +
> + /* Switch back to the thread stack and restore ra and s0 */
> + addi sp, s0, -STACKFRAME_SIZE_ON_STACK
> + REG_L ra, STACKFRAME_RA(sp)
> + REG_L s0, STACKFRAME_FP(sp)
> + addi sp, sp, STACKFRAME_SIZE_ON_STACK
> +
> + ret
> +SYM_FUNC_END(call_on_irq_stack)
> +#endif /* CONFIG_IRQ_STACKS */
> +
> /*
> * Integer register context switch
> * The callee-saved registers must be saved and restored.
> diff --git a/arch/riscv/kernel/irq.c b/arch/riscv/kernel/irq.c
> index a8efa053c4a5..95dafdcbd135 100644
> --- a/arch/riscv/kernel/irq.c
> +++ b/arch/riscv/kernel/irq.c
> @@ -61,35 +61,16 @@ static void init_irq_stacks(void)
> #endif /* CONFIG_VMAP_STACK */
>
> #ifdef CONFIG_HAVE_SOFTIRQ_ON_OWN_STACK
> +static void ___do_softirq(struct pt_regs *regs)
> +{
> + __do_softirq();
> +}
> +
> void do_softirq_own_stack(void)
> {
> -#ifdef CONFIG_IRQ_STACKS
> - if (on_thread_stack()) {
> - ulong *sp = per_cpu(irq_stack_ptr, smp_processor_id())
> - + IRQ_STACK_SIZE/sizeof(ulong);
> - __asm__ __volatile(
> - "addi sp, sp, -"RISCV_SZPTR "\n"
> - REG_S" ra, (sp) \n"
> - "addi sp, sp, -"RISCV_SZPTR "\n"
> - REG_S" s0, (sp) \n"
> - "addi s0, sp, 2*"RISCV_SZPTR "\n"
> - "move sp, %[sp] \n"
> - "call __do_softirq \n"
> - "addi sp, s0, -2*"RISCV_SZPTR"\n"
> - REG_L" s0, (sp) \n"
> - "addi sp, sp, "RISCV_SZPTR "\n"
> - REG_L" ra, (sp) \n"
> - "addi sp, sp, "RISCV_SZPTR "\n"
> - :
> - : [sp] "r" (sp)
> - : "a0", "a1", "a2", "a3", "a4", "a5", "a6", "a7",
> - "t0", "t1", "t2", "t3", "t4", "t5", "t6",
> -#ifndef CONFIG_FRAME_POINTER
> - "s0",
> -#endif
> - "memory");
> - } else
> -#endif
> + if (on_thread_stack())
> + call_on_irq_stack(NULL, ___do_softirq);
> + else
> __do_softirq();
> }
> #endif /* CONFIG_HAVE_SOFTIRQ_ON_OWN_STACK */
> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> index a05905d88802..1fe6b475cdfb 100644
> --- a/arch/riscv/kernel/traps.c
> +++ b/arch/riscv/kernel/traps.c
> @@ -350,34 +350,10 @@ static void noinstr handle_riscv_irq(struct pt_regs *regs)
> asmlinkage void noinstr do_irq(struct pt_regs *regs)
> {
> irqentry_state_t state = irqentry_enter(regs);
> -#ifdef CONFIG_IRQ_STACKS
> - if (on_thread_stack()) {
> - ulong *sp = per_cpu(irq_stack_ptr, smp_processor_id())
> - + IRQ_STACK_SIZE/sizeof(ulong);
> - __asm__ __volatile(
> - "addi sp, sp, -"RISCV_SZPTR "\n"
> - REG_S" ra, (sp) \n"
> - "addi sp, sp, -"RISCV_SZPTR "\n"
> - REG_S" s0, (sp) \n"
> - "addi s0, sp, 2*"RISCV_SZPTR "\n"
> - "move sp, %[sp] \n"
> - "move a0, %[regs] \n"
> - "call handle_riscv_irq \n"
> - "addi sp, s0, -2*"RISCV_SZPTR"\n"
> - REG_L" s0, (sp) \n"
> - "addi sp, sp, "RISCV_SZPTR "\n"
> - REG_L" ra, (sp) \n"
> - "addi sp, sp, "RISCV_SZPTR "\n"
> - :
> - : [sp] "r" (sp), [regs] "r" (regs)
> - : "a0", "a1", "a2", "a3", "a4", "a5", "a6", "a7",
> - "t0", "t1", "t2", "t3", "t4", "t5", "t6",
> -#ifndef CONFIG_FRAME_POINTER
> - "s0",
> -#endif
> - "memory");
> - } else
> -#endif
> +
> + if (IS_ENABLED(CONFIG_IRQ_STACKS) && on_thread_stack())
> + call_on_irq_stack(regs, handle_riscv_irq);
A good code optimization for maintenance.

Reviewed-by: Guo Ren <guoren@kernel.org>

> + else
> handle_riscv_irq(regs);
>
> irqentry_exit(regs, state);
> --
> 2.42.0.rc2.253.gd59a3bf2b4-goog
>

--
Best Regards
Guo Ren