[Bug 206579] KVM with passthrough generates "BUG: kernel NULL pointer dereference" and crashes

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https://bugzilla.kernel.org/show_bug.cgi?id=206579

--- Comment #61 from muncrief (rmuncrief@humanavance.com) ---
(In reply to Anthony from comment #60)
> To add hiding cpu id hypervisor seems to also cause it to not work well.
> Windows also generally don't perform as well when hiding the hypervisor CPU
> id on Ryzen.
> 
> Using top we see high activity in avic_vcpu_put.part.0 & avic_vcpu_load
> functions and near-zero to zero activity with svm_deliver_avic_intr
> function. Which suggests AVIC isn't working correctly if my sight
> understanding of svm_deliver_avic_intr function is correct.
> 
> Haven't looked to in-depth but I would guess SVM/AVIC uses hypervisor cpuid
> as check? to apply its optimizations or something along those lines.

I can't unhide the hypervisor because I have a cheap Nvidia GT 710 for the VM
and it won't work unless the hypervisor is hidden.

However I did use the other techniques to verify whether AVIC was working or
not, and it definitely is not. There were 0 AVIC events no matter what I tried.

By the way, I tested with both 5.7 rc1 and rc2 and neither works. Thank you for
the suggestions though. So unless there's something else someone wants me to
try I'll test things again Sunday when rc3 is released.

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