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To:     guoren@kernel.org, arnd@arndb.de, guoren@kernel.org,
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Cc:     linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-riscv@lists.infradead.org, Guo Ren <guoren@linux.alibaba.com>
Subject: Re: [PATCH -next V10 09/10] riscv: stack: Support
 HAVE_SOFTIRQ_ON_OWN_STACK
In-Reply-To: <20221208025816.138712-10-guoren@kernel.org>
References: <20221208025816.138712-1-guoren@kernel.org>
 <20221208025816.138712-10-guoren@kernel.org>
Date:   Thu, 08 Dec 2022 11:12:21 +0100
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guoren@kernel.org writes:

> From: Guo Ren <guoren@linux.alibaba.com>
>
> Add the HAVE_SOFTIRQ_ON_OWN_STACK feature for the IRQ_STACKS config. The
> irq and softirq use the same independent irq_stack of percpu by time
> division multiplexing.
>
> Tested-by: Jisheng Zhang <jszhang@kernel.org>
> Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> Signed-off-by: Guo Ren <guoren@kernel.org>
> ---
>  arch/riscv/Kconfig      |  7 ++++---
>  arch/riscv/kernel/irq.c | 33 +++++++++++++++++++++++++++++++++
>  2 files changed, 37 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 0a9d4bdc0338..bd4c4ae4cdc9 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -447,12 +447,13 @@ config FPU
>  	  If you don't know what to do here, say Y.
>=20=20
>  config IRQ_STACKS
> -	bool "Independent irq stacks" if EXPERT
> +	bool "Independent irq & softirq stacks" if EXPERT
>  	default y
>  	select HAVE_IRQ_EXIT_ON_IRQ_STACK
> +	select HAVE_SOFTIRQ_ON_OWN_STACK

HAVE_IRQ_EXIT_ON_IRQ_STACK is used by softirq.c Shouldn't that be
selected introduced in this patch, instead of the previous one?

>  	help
> -	  Add independent irq stacks for percpu to prevent kernel stack overflo=
ws.
> -	  We may save some memory footprint by disabling IRQ_STACKS.
> +	  Add independent irq & softirq stacks for percpu to prevent kernel sta=
ck
> +	  overflows. We may save some memory footprint by disabling IRQ_STACKS.

Same comment from previous patch. Please use the same wording/config as
other archs.

>  endmenu # "Platform type"
>=20=20
> diff --git a/arch/riscv/kernel/irq.c b/arch/riscv/kernel/irq.c
> index 5d77f692b198..a6406da34937 100644
> --- a/arch/riscv/kernel/irq.c
> +++ b/arch/riscv/kernel/irq.c
> @@ -11,6 +11,7 @@
>  #include <linux/seq_file.h>
>  #include <asm/smp.h>
>  #include <asm/vmap_stack.h>
> +#include <asm/softirq_stack.h>
>=20=20
>  #ifdef CONFIG_IRQ_STACKS
>  static DEFINE_PER_CPU(ulong *, irq_stack_ptr);
> @@ -38,6 +39,38 @@ static void init_irq_stacks(void)
>  		per_cpu(irq_stack_ptr, cpu) =3D per_cpu(irq_stack, cpu);
>  }
>  #endif /* CONFIG_VMAP_STACK */
> +
> +#ifdef CONFIG_HAVE_SOFTIRQ_ON_OWN_STACK
> +void do_softirq_own_stack(void)
> +{
> +#ifdef CONFIG_IRQ_STACKS
> +	if (on_thread_stack()) {
> +		ulong *sp =3D 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",
> +		  "memory");

Same as previous patch. Please avoid C&P and have a look at how
call_on_stack is done on x86.


Bj=C3=B6rn