linux-kernel - Re: [PATCH RFC] KVM: x86: vmx: throttle immediate exit through preemtion timer to assist buggy guests

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Message-ID: <87lg0u0zyo.fsf@vitty.brq.redhat.com>
Date:   Mon, 01 Apr 2019 12:41:51 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Liran Alon <liran.alon@...cle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        Radim Krčmář <rkrcmar@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] KVM: x86: vmx: throttle immediate exit through preemtion timer to assist buggy guests

Liran Alon <liran.alon@...cle.com> writes:

> So to sum-up: This matches what I mentioned in my previous emails right?
> That vector 96 is not related, and the only issue here is that level-triggered interrupt handler for vector 80 is doing EOI before lowering the irq-line.
> Which cause vector 80 to be injected in infinite loop.
> And this is not even related to being a nested virtualization
> workload. It’s just an issue in Hyper-V (L1) interrupt handler for
> vector 80.

Yes, it may be related to how communications between Hyper-V and Windows
partition are organized but it's a pure speculation.

>
> Therefore the only action-items are:
> 1) Microsoft to fix Hyper-V vector 80 interrupt handler to lower irq-line before EOI.
> 2) Patch QEMU IOAPIC implementation to have a mechanism similar to KVM to delay injection of level-triggered interrupt
>     in case we are injecting the same interrupt for X times in a row.

I'm intended to do 2) and we already let MS know there's an issue.

Thanks for your help with the investigation guys!

-- 
Vitaly