linux-kernel - Re: [patch V6 08/37] x86/entry/64: Move do_softirq_own

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Date:   Mon, 18 May 2020 16:48:54 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Wei Liu <wei.liu@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Jason Chen CJ <jason.cj.chen@...el.com>,
        Zhao Yakui <yakui.zhao@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [patch V6 08/37] x86/entry/64: Move do_softirq_own_stack() to C

On Fri, May 15, 2020 at 5:10 PM Thomas Gleixner <tglx@...utronix.de> wrote:
>
>
> The first step to get rid of the ENTER/LEAVE_IRQ_STACK ASM macro maze.  Use
> the new C code helpers to move do_softirq_own_stack() out of ASM code.
>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
>
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index 3b8da9f09297..bdf8391b2f95 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -1145,19 +1145,6 @@ SYM_FUNC_START(asm_call_on_stack)
>         ret
>  SYM_FUNC_END(asm_call_on_stack)
>
> -/* Call softirq on interrupt stack. Interrupts are off. */
> -.pushsection .text, "ax"
> -SYM_FUNC_START(do_softirq_own_stack)
> -       pushq   %rbp
> -       mov     %rsp, %rbp
> -       ENTER_IRQ_STACK regs=0 old_rsp=%r11
> -       call    __do_softirq
> -       LEAVE_IRQ_STACK regs=0
> -       leaveq
> -       ret
> -SYM_FUNC_END(do_softirq_own_stack)
> -.popsection
> -
>  #ifdef CONFIG_XEN_PV
>  /*
>   * A note on the "critical region" in our callback handler.
> diff --git a/arch/x86/kernel/irq_64.c b/arch/x86/kernel/irq_64.c
> index 12df3a4abfdd..62cff52e03c5 100644
> --- a/arch/x86/kernel/irq_64.c
> +++ b/arch/x86/kernel/irq_64.c
> @@ -20,6 +20,7 @@
>  #include <linux/sched/task_stack.h>
>
>  #include <asm/cpu_entry_area.h>
> +#include <asm/irq_stack.h>
>  #include <asm/io_apic.h>
>  #include <asm/apic.h>
>
> @@ -70,3 +71,11 @@ int irq_init_percpu_irqstack(unsigned int cpu)
>                 return 0;
>         return map_irq_stack(cpu);
>  }
> +
> +void do_softirq_own_stack(void)
> +{
> +       if (irqstack_active())
> +               __do_softirq();
> +       else
> +               run_on_irqstack(__do_softirq, NULL);
> +}

See my comment in patch 8.  I see no great reason that this should
open-code the conditional, except maybe that we don't have pt_regs
here so the condition needs to be a bit different.