On 29/03/19 15:40, Vitaly Kuznetsov wrote:
> Paolo Bonzini <pbonzini@xxxxxxxxxx> writes:
>
>> On 28/03/19 21:31, Vitaly Kuznetsov wrote:
>>>
>>> The 'hang' scenario develops like this:
>>> 1) Hyper-V boots and QEMU is trying to inject two irq simultaneously. One
>>> of them is level-triggered. KVM injects the edge-triggered one and
>>> requests immediate exit to inject the level-triggered:
>>>
>>> kvm_set_irq: gsi 23 level 1 source 0
>>> kvm_msi_set_irq: dst 0 vec 80 (Fixed|physical|level)
>>> kvm_apic_accept_irq: apicid 0 vec 80 (Fixed|edge)
>>> kvm_msi_set_irq: dst 0 vec 96 (Fixed|physical|edge)
>>> kvm_apic_accept_irq: apicid 0 vec 96 (Fixed|edge)
>>> kvm_nested_vmexit_inject: reason EXTERNAL_INTERRUPT info1 0 info2 0 int_info 80000060 int_info_err 0
>>>
>>> 2) Hyper-V requires one of its VMs to run to handle the situation but
>>> immediate exit happens:
>>>
>>> kvm_entry: vcpu 0
>>> kvm_exit: reason VMRESUME rip 0xfffff80006a40115 info 0 0
>>> kvm_entry: vcpu 0
>>> kvm_exit: reason PREEMPTION_TIMER rip 0xfffff8022f3d8350 info 0 0
>>> kvm_nested_vmexit: rip fffff8022f3d8350 reason PREEMPTION_TIMER info1 0 info2 0 int_info 0 int_info_err 0
>>> kvm_nested_vmexit_inject: reason EXTERNAL_INTERRUPT info1 0 info2 0 int_info 80000050 int_info_err 0
>>
>> I supposed before this there was an eoi for vector 96?
>
> AFAIR: no, it seems that it is actually the VM it is trying to resume
> (Windows partition?) which needs to do some work and with the preemtion
> timer of 0 we don't allow it to.
kvm_apic_accept_irq placed IRQ 96 in IRR, and Hyper-V should be running
with "acknowledge interrupt on exit" since int_info is nonzero in
kvm_nested_vmexit_inject.
Therefore, at the kvm_nested_vmexit_inject tracepoint KVM should have
set bit 96 in ISR; and because PPR is now 96, interrupt 80 should have
never been delivered. Unless 96 is an auto-EOI interrupt, in which case
this comment would apply
/*
* For auto-EOI interrupts, there might be another pending
* interrupt above PPR, so check whether to raise another
* KVM_REQ_EVENT.
*/
IIRC there was an enlightenment to tell Windows "I support auto-EOI but
please don't use it". If this is what's happening, that would also fix it.
Thanks,
Paolo
