From: Mark Rutland <mark.rutland@arm.com>
To: Pingfan Liu <kernelfans@gmail.com>
Cc: linux-arm-kernel@lists.infradead.org,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
Joey Gouly <joey.gouly@arm.com>,
Sami Tolvanen <samitolvanen@google.com>,
Julien Thierry <julien.thierry@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Yuichi Ito <ito-yuichi@fujitsu.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCHv2 1/5] arm64/entry-common: push the judgement of nmi ahead
Date: Thu, 30 Sep 2021 14:32:57 +0100 [thread overview]
Message-ID: <20210930133257.GB18258@lakrids.cambridge.arm.com> (raw)
In-Reply-To: <YU9Cy9kTew4ySeGZ@piliu.users.ipa.redhat.com>
On Sat, Sep 25, 2021 at 11:39:55PM +0800, Pingfan Liu wrote:
> On Fri, Sep 24, 2021 at 06:53:06PM +0100, Mark Rutland wrote:
> > On Fri, Sep 24, 2021 at 09:28:33PM +0800, Pingfan Liu wrote:
> > > In enter_el1_irq_or_nmi(), it can be the case which NMI interrupts an
> > > irq, which makes the condition !interrupts_enabled(regs) fail to detect
> > > the NMI. This will cause a mistaken account for irq.
> >
> Sorry about the confusing word "account", it should be "lockdep/rcu/.."
>
> > Can you please explain this in more detail? It's not clear which
> > specific case you mean when you say "NMI interrupts an irq", as that
> > could mean a number of distinct scenarios.
> >
> > AFAICT, if we're in an IRQ handler (with NMIs unmasked), and an NMI
> > causes a new exception we'll do the right thing. So either I'm missing a
> > subtlety or you're describing a different scenario..
> >
> > Note that the entry code is only trying to distinguish between:
> >
> > a) This exception is *definitely* an NMI (because regular interrupts
> > were masked).
> >
> > b) This exception is *either* and IRQ or an NMI (and this *cannot* be
> > distinguished until we acknowledge the interrupt), so we treat it as
> > an IRQ for now.
> >
> b) is the aim.
>
> At the entry, enter_el1_irq_or_nmi() -> enter_from_kernel_mode()->rcu_irq_enter()/rcu_irq_enter_check_tick() etc.
> While at irqchip level, gic_handle_irq()->gic_handle_nmi()->nmi_enter(),
> which does not call rcu_irq_enter_check_tick(). So it is not proper to
> "treat it as an IRQ for now"
I'm struggling to understand the problem here. What is "not proper", and
why?
Do you think there's a correctness problem, or that we're doing more
work than necessary?
If you could give a specific example of a problem, it would really help.
I'm aware that we do more work than strictly necessary when we take a
pNMI from a context with IRQs enabled, but that's how we'd intended this
to work, as it's vastly simpler to manage the state that way. Unless
there's a real problem with that approach I'd prefer to leave it as-is.
Thanks,
Mark.
next prev parent reply other threads:[~2021-09-30 13:33 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-24 13:28 [PATCHv2 0/5] arm64/irqentry: remove duplicate housekeeping of Pingfan Liu
2021-09-24 13:28 ` [PATCHv2 1/5] arm64/entry-common: push the judgement of nmi ahead Pingfan Liu
2021-09-24 17:53 ` Mark Rutland
2021-09-25 15:39 ` Pingfan Liu
2021-09-30 13:32 ` Mark Rutland [this message]
2021-10-08 4:01 ` Pingfan Liu
2021-10-08 14:55 ` Pingfan Liu
2021-10-08 17:25 ` Mark Rutland
2021-10-09 3:49 ` Pingfan Liu
2021-10-08 15:45 ` Paul E. McKenney
2021-10-09 4:14 ` Pingfan Liu
2021-09-24 13:28 ` [PATCHv2 2/5] irqchip/GICv3: expose handle_nmi() directly Pingfan Liu
2021-09-24 13:28 ` [PATCHv2 3/5] kernel/irq: make irq_{enter,exit}() in handle_domain_irq() arch optional Pingfan Liu
2021-09-28 8:55 ` Mark Rutland
2021-09-29 3:15 ` Pingfan Liu
2021-09-24 13:28 ` [PATCHv2 4/5] irqchip/GICv3: let gic_handle_irq() utilize irqentry on arm64 Pingfan Liu
2021-09-28 9:10 ` Mark Rutland
2021-09-29 3:10 ` Pingfan Liu
2021-09-29 7:20 ` Marc Zyngier
2021-09-29 8:27 ` Pingfan Liu
2021-09-29 9:23 ` Mark Rutland
2021-09-29 11:40 ` Pingfan Liu
2021-09-29 14:29 ` Pingfan Liu
2021-09-29 17:41 ` Mark Rutland
2021-09-24 13:28 ` [PATCHv2 5/5] irqchip/GICv3: make reschedule-ipi light weight Pingfan Liu
2021-09-29 7:24 ` Marc Zyngier
2021-09-29 8:32 ` Pingfan Liu
2021-09-24 17:36 ` [PATCHv2 0/5] arm64/irqentry: remove duplicate housekeeping of Mark Rutland
2021-09-24 22:59 ` Paul E. McKenney
2021-09-27 9:23 ` Mark Rutland
2021-09-28 0:09 ` Paul E. McKenney
2021-09-28 8:32 ` Mark Rutland
2021-09-28 8:35 ` Mark Rutland
2021-09-28 9:52 ` Sven Schnelle
2021-09-28 10:26 ` Mark Rutland
2021-09-28 13:55 ` Paul E. McKenney
2021-09-25 15:12 ` Pingfan Liu
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