linux-kernel - Re: [PATCH] KVM: x86: call irq notifiers with directed EOI

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Date:	Fri, 20 Mar 2015 15:43:02 +0100
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Paolo Bonzini <pbonzini@...hat.com>, chao.zhou@...el.com
Subject: Re: [PATCH] KVM: x86: call irq notifiers with directed EOI

2015-03-19 18:44-0300, Marcelo Tosatti:
> On Wed, Mar 18, 2015 at 07:38:22PM +0100, Radim Krčmář wrote:
> > kvm_ioapic_update_eoi() wasn't called if directed EOI was enabled.
> > We need to do that for irq notifiers.  (Like with edge interrupts.)
> > 
> > Fix it by skipping EOI broadcast only.
> > 
> > Bug: https://bugzilla.kernel.org/show_bug.cgi?id=82211
> > Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
> > ---
> > diff --git a/arch/x86/kvm/ioapic.c b/arch/x86/kvm/ioapic.c
> > @@ -443,7 +444,8 @@ static void __kvm_ioapic_update_eoi(struct kvm_vcpu *vcpu,
> > -		if (trigger_mode != IOAPIC_LEVEL_TRIG)
> > +		if (trigger_mode != IOAPIC_LEVEL_TRIG ||
> > +		    kvm_apic_get_reg(apic, APIC_SPIV) & APIC_SPIV_DIRECTED_EOI)
> >  			continue;
> 
> Don't you have to handle kvm_ioapic_eoi_inject_work as well?

It works without that: ent->fields.remote_irr == 1, thus
kvm_ioapic_eoi_inject_work() will do nothing.
Adding a check would be better for clarity, though.

We could add the EOI register (implement IO-APIC version 0x20), because
kernels are forced to do ugly hacks otherwise (switching to
edge-triggered mode and back).
We also clear remote_irr on a different occasion (just a write to
ioreg).

I'll take a closer look at the second one.

> >  		ASSERT(ent->fields.trig_mode == IOAPIC_LEVEL_TRIG);
> 
> This assert can now fail?

I think it can't (nothing changed), but that is how asserts should be.
It checks a different variable than the condition above.
('trigger_mode' is sourced from APIC_TMR, which should correctly match
 'ent->fields.trig_mode'.)

The assert would be more useful before 'continue;', and modified:
  ASSERT(ent->fields.trig_mode == trigger_mode)

Thanks for the review, I'll incorporate the your comments to v2.
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