linux-kernel - Re: [BUG] kvm: APIC emulation problem

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Date:   Tue, 2 Jul 2019 08:40:32 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Wanpeng Li <kernellwp@...il.com>
cc:     Rong Chen <rong.a.chen@...el.com>, Feng Tang <feng.tang@...el.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "tipbuild@...or.com" <tipbuild@...or.com>,
        "lkp@...org" <lkp@...org>, Ingo Molnar <mingo@...nel.org>,
        kvm <kvm@...r.kernel.org>, Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Fenghua Yu <fenghua.yu@...el.com>
Subject: Re: [BUG] kvm: APIC emulation problem - was Re: [LKP] [x86/hotplug]
 ...

Wanpeng,

On Tue, 2 Jul 2019, Wanpeng Li wrote:
> On Tue, 2 Jul 2019 at 06:44, Thomas Gleixner <tglx@...utronix.de> wrote:
> >
> > While that CPU0 hotplug test case is surely an esoteric issue, the APIC
> > emulation is still wrong, Even if the play_dead() code would not enable
> > interrupts then the pending IRR bit would turn into an ISR .. interrupt
> > when the APIC is reenabled on startup.
> 
> >From SDM 10.4.7.2 Local APIC State After It Has Been Software Disabled
> * Pending interrupts in the IRR and ISR registers are held and require
> masking or handling by the CPU.

Correct.
 
> In your testing, hardware cpu will not respect soft disable APIC when
> IRR has already been set or APICv posted-interrupt is in flight, so we
> can skip soft disable APIC checking when clearing IRR and set ISR,
> continue to respect soft disable APIC when attempting to set IRR.
> Could you try below fix?

> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 05d8934..f857a12 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -2376,7 +2376,7 @@ int kvm_apic_has_interrupt(struct kvm_vcpu *vcpu)
>      struct kvm_lapic *apic = vcpu->arch.apic;
>      u32 ppr;
> 
> -    if (!apic_enabled(apic))
> +    if (!kvm_apic_hw_enabled(apic))
>          return -1;
> 
>      __apic_update_ppr(apic, &ppr);

Yes. That fixes it and works as expected. Thanks for the quick
resolution. I surely stared at that function, but was not sure how to fix
it proper.

Tested-by: Thomas Gleixner <tglx@...utronix.de>

Please add a Cc: stable... tag when you post the patch.

Thanks,

	tglx