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

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Date:   Fri, 1 Oct 2021 22:12:44 +0800
From:   Pingfan Liu <kernelfans@...il.com>
To:     Marc Zyngier <maz@...nel.org>
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 Fri, Oct 01, 2021 at 10:21:06AM +0100, Marc Zyngier wrote:
> 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.
> 
OK, I will fix it.

> >  }
> >  
> >  asmlinkage void noinstr el1h_64_irq_handler(struct pt_regs *regs)
> 
> With Mark's remark addressed,
> 
> Reviewed-by: Marc Zyngier <maz@...nel.org>
> 
Thanks,

	Pingfan