linux-kernel - Re: [PATCHv3 2/3] arm64: entry: refactor EL1 interrupt entry logic

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Message-ID: <87r1d5rth9.wl-maz@kernel.org>
Date:   Fri, 01 Oct 2021 10:21:06 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Pingfan Liu <kernelfans@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Mark Rutland <mark.rutland@....com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Joey Gouly <joey.gouly@....com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Julien Thierry <julien.thierry@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yuichi Ito <ito-yuichi@...itsu.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 2/3] arm64: entry: refactor EL1 interrupt entry logic

On Thu, 30 Sep 2021 14:17:07 +0100,
Pingfan Liu <kernelfans@...il.com> wrote:
> 
> From: Mark Rutland <mark.rutland@....com>
> 
> Currently we distinguish IRQ and definitely-PNMI at entry/exit time
> via the enter_el1_irq_or_nmi() and enter_el1_irq_or_nmi() helpers. In
> subsequent patches we'll need to handle the two cases more distinctly
> in the body of the exception handler.
> 
> To make this possible, this patch refactors el1_interrupt to be a
> top-level dispatcher to separate handlers for the IRQ and PNMI cases,
> removing the need for the enter_el1_irq_or_nmi() and
> exit_el1_irq_or_nmi() helpers.
> 
> Note that since arm64_enter_nmi() calls __nmi_enter(), which
> increments the preemt_count, we could never preempt when handling a
> PNMI. We now only check for preemption in the IRQ case, which makes
> this clearer.
> 
> There should be no functional change as a result of this patch.
> 
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Cc: "Paul E. McKenney" <paulmck@...nel.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Joey Gouly <joey.gouly@....com>
> Cc: Sami Tolvanen <samitolvanen@...gle.com>
> Cc: Julien Thierry <julien.thierry@....com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Yuichi Ito <ito-yuichi@...itsu.com>
> Cc: Pingfan Liu <kernelfans@...il.com>
> Cc: linux-kernel@...r.kernel.org
> To: linux-arm-kernel@...ts.infradead.org
> ---
>  arch/arm64/kernel/entry-common.c | 44 ++++++++++++++++----------------
>  1 file changed, 22 insertions(+), 22 deletions(-)
> 
> diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
> index 32f9796c4ffe..5f1473319fb0 100644
> --- a/arch/arm64/kernel/entry-common.c
> +++ b/arch/arm64/kernel/entry-common.c
> @@ -219,22 +219,6 @@ static void noinstr arm64_exit_el1_dbg(struct pt_regs *regs)
>  		lockdep_hardirqs_on(CALLER_ADDR0);
>  }
>  
> -static void noinstr enter_el1_irq_or_nmi(struct pt_regs *regs)
> -{
> -	if (IS_ENABLED(CONFIG_ARM64_PSEUDO_NMI) && !interrupts_enabled(regs))
> -		arm64_enter_nmi(regs);
> -	else
> -		enter_from_kernel_mode(regs);
> -}
> -
> -static void noinstr exit_el1_irq_or_nmi(struct pt_regs *regs)
> -{
> -	if (IS_ENABLED(CONFIG_ARM64_PSEUDO_NMI) && !interrupts_enabled(regs))
> -		arm64_exit_nmi(regs);
> -	else
> -		exit_to_kernel_mode(regs);
> -}
> -
>  static void __sched arm64_preempt_schedule_irq(void)
>  {
>  	lockdep_assert_irqs_disabled();
> @@ -432,14 +416,19 @@ asmlinkage void noinstr el1h_64_sync_handler(struct pt_regs *regs)
>  	}
>  }
>  
> -static void noinstr el1_interrupt(struct pt_regs *regs,
> -				  void (*handler)(struct pt_regs *))
> +static __always_inline void
> +__el1_pnmi(struct pt_regs *regs, void (*handler)(struct pt_regs *))
>  {
> -	write_sysreg(DAIF_PROCCTX_NOIRQ, daif);
> -
> -	enter_el1_irq_or_nmi(regs);
> +	arm64_enter_nmi(regs);
>  	do_interrupt_handler(regs, handler);
> +	arm64_exit_nmi(regs);
> +}
>  
> +static __always_inline void
> +__el1_interrupt(struct pt_regs *regs, void (*handler)(struct pt_regs *))
> +{
> +	enter_from_kernel_mode(regs);
> +	do_interrupt_handler(regs, handler);
>  	/*
>  	 * Note: thread_info::preempt_count includes both thread_info::count
>  	 * and thread_info::need_resched, and is not equivalent to
> @@ -448,8 +437,19 @@ static void noinstr el1_interrupt(struct pt_regs *regs,
>  	if (IS_ENABLED(CONFIG_PREEMPTION) &&
>  	    READ_ONCE(current_thread_info()->preempt_count) == 0)
>  		arm64_preempt_schedule_irq();
> +	exit_to_kernel_mode(regs);
> +}
> +
> +static void noinstr el1_interrupt(struct pt_regs *regs,
> +				  void (*handler)(struct pt_regs *))
> +{
> +	write_sysreg(DAIF_PROCCTX_NOIRQ, daif);
> +
> +	if (IS_ENABLED(CONFIG_ARM64_PSEUDO_NMI) && !interrupts_enabled(regs))
> +		__el1_pnmi(regs, handler);
> +	else
> +		__el1_interrupt(regs, handler);
>  
> -	exit_el1_irq_or_nmi(regs);

nit: spurious blank line.

>  }
>  
>  asmlinkage void noinstr el1h_64_irq_handler(struct pt_regs *regs)

With Mark's remark addressed,

Reviewed-by: Marc Zyngier <maz@...nel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.