linux-kernel - Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry

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Date:   Thu, 3 Nov 2016 19:29:31 +0100
From:   Radim Krčmář <rkrcmar@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        yang.zhang.wz@...il.com, feng.wu@...el.com, mst@...hat.com
Subject: Re: [PATCH 2/5] KVM: x86: do not scan IRR twice on APICv vmentry

2016-11-03 19:18+0100, Paolo Bonzini:
> On 03/11/2016 19:07, Radim Krčmář wrote:
>> 2016-11-03 17:00+0100, Paolo Bonzini:
>>> On 03/11/2016 16:03, Radim Krčmář wrote:
>>>> 2016-11-03 14:30+0100, Paolo Bonzini:
>>>>> On 26/10/2016 21:59, Radim Krčmář wrote:
>>>>>> 2016-10-14 20:21+0200, Paolo Bonzini:
>>>>>>> Calling apic_find_highest_irr results in IRR being scanned twice,
>>>>>>> once in vmx_sync_pir_from_irr and once in apic_search_irr.  Change
>>>>>>> sync_pir_from_irr to do the RVI write and kvm_apic_update_irr to
>>>>>>> compute the new RVI on the fly.
>>>>>>>
>>>>>>> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
>>>>>>> ---
>>>>>>
>>>>>> Reviewed-by: Radim Krčmář <rkrcmar@...hat.com>
>>>>>
>>>>> Nope, this breaks nested VMX exit on external interrupt.  For now I'm
>>>>> testing only patch 1 and will push that one only to kvm/next.
>> 
>> Which hypervisor is being nested?
> 
> vmx.flat. :)
> 
>> I think a bug is likely for hypervisors that don't enable
>> PIN_BASED_EXT_INTR_MASK.  The bug would trigger when
>> kvm_cpu_has_interrupt() in vmx_check_nested_events() in
>> kvm_arch_vcpu_runnable() queues the interrupt ...
>> but I didn't see how this would have caused a problem. :)
> 
> Ironically, _not_ enabling PIN_BASED_EXT_INTR_MASK and not using HALT
> activity state is the only case that passes of the four that vmx.flat tests.

Heh, the behavior is nice

PASS: direct interrupt + hlt
FAIL: intercepted interrupt + hlt
FAIL: direct interrupt + activity state hlt
FAIL: intercepted interrupt + activity state hlt