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From:   bugzilla-daemon@bugzilla.kernel.org
To:     kvm@vger.kernel.org
Subject: [Bug 206579] KVM with passthrough generates "BUG: kernel NULL
 pointer dereference" and crashes
Date:   Tue, 25 Feb 2020 08:53:25 +0000
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https://bugzilla.kernel.org/show_bug.cgi?id=206579

--- Comment #21 from Suravee Suthikulpanit (suravee.suthikulpanit@amd.com) ---
Paolo/Muncrief,

I have also finally reproduce the issue (w/ -machine kernel_irqchip=off). The
the recommended changes (w/ if (!avic || !irqchip_in_kernel(svm->vcpu.kvm))
fixes the issue. Thanks for catching this.

Paolo, If the NULL pointer is due to:

    if (!svm->vcpu.arch.apic->regs)
        return -EINVAL;

Shouldn't we be checking the following instead:

    if (!avic || !lapic_in_kernel(&svm->vcpu))
        return 0;

This also works in my test.

Muncrief,

Besides enabling AVIC (modprobe kvm_amd avic=1), you can check to see if AVIC
is activated for the VM by running "perf kvm stat live" while running the VM
and see if there are any AVIC-related #vmexits (instead of vintr).

Thanks,
Suravee

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