Messages in this thread | | | Date | Thu, 30 Sep 2021 14:32:57 +0100 | From | Mark Rutland <> | Subject | Re: [PATCHv2 1/5] arm64/entry-common: push the judgement of nmi ahead |
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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.
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