Re: [PATCH] KVM: x86: reset RVI upon system reset

["Chen, Tiejun" <tiejun.chen@intel.com>]

On 2014/11/5 16:50, Wang, Wei W wrote:
> On 05/11/2014 4:07, Tiejun Chen wrote:
>>>>> A bug was reported as follows: when running Windows 7 32-bit guests
>>>>> on qemu-kvm, sometimes the guests run into blue screen during
>>>>> reboot. The problem was that a guest's RVI was not cleared when it
>>>>> rebooted. This
>>>> patch has fixed the problem.
>>>>>
>>>>> Signed-off-by: Wei Wang <wei.w.wang@intel.com>
>>>>> Signed-off-by: Yang Zhang <yang.z.zhang@intel.com>
>>>>> Tested-by: Rongrong Liu <rongrongx.liu@intel.com>, Da Chun
>>>>> <ngugc@qq.com>
>>>>> ---
>>>>>     arch/x86/kvm/lapic.c |    3 +++
>>>>>     arch/x86/kvm/vmx.c   |   12 ++++++------
>>>>>     2 files changed, 9 insertions(+), 6 deletions(-)
>>>>>
>>>>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index
>>>>> 66dd173..6942742 100644
>>>>> --- a/arch/x86/kvm/lapic.c
>>>>> +++ b/arch/x86/kvm/lapic.c
>>>>> @@ -1712,6 +1712,9 @@ void kvm_apic_post_state_restore(struct
>>>> kvm_vcpu *vcpu,
>>>>>     	apic->isr_count = kvm_apic_vid_enabled(vcpu->kvm) ?
>>>>>     				1 : count_vectors(apic->regs + APIC_ISR);
>>>>>     	apic->highest_isr_cache = -1;
>>>>> +	if (kvm_x86_ops->hwapic_irr_update)
>>>>> +		kvm_x86_ops->hwapic_irr_update(vcpu,
>>>>> +				apic_find_highest_irr(apic));
>>>>
>>>> Could we pass 0 directly? Because looks we just need to clear RVI.
>>>>
>>>> kvm_x86_ops->hwapic_irr_update(vcpu, 0);
>>>>
>>>> I think this already makes sense based on your description.
>>>>
>>>> Thanks
>>>> Tiejun
>>>
>>> No. This is a restore function, and we cannot assume that the callers
>> always need to reset to the initial state.
>>
>> Okay. Maybe I'm confused by the following change.
>>
>>>
>>> Wei
>>>>
>>>>>     	kvm_x86_ops->hwapic_isr_update(vcpu->kvm,
>>>> apic_find_highest_isr(apic));
>>>>>     	kvm_make_request(KVM_REQ_EVENT, vcpu);
>>>>>     	kvm_rtc_eoi_tracking_restore_one(vcpu);
>>>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index
>>>>> fe4d2f4..d632548 100644
>>>>> --- a/arch/x86/kvm/vmx.c
>>>>> +++ b/arch/x86/kvm/vmx.c
>>>>> @@ -7292,19 +7292,19 @@ static void vmx_set_rvi(int vector)
>>>>>     static void vmx_hwapic_irr_update(struct kvm_vcpu *vcpu, int max_irr)
>>>>>     {
>>>>>     	if (max_irr == -1)
>>>>> +		max_irr = 0;
>>>>> +
>>>>> +	if (!is_guest_mode(vcpu)) {
>>>>> +		vmx_set_rvi(max_irr);
>>>>>     		return;
>>>>> +	}
>>>>>
>>>>>     	/*
>>>>>     	 * If a vmexit is needed, vmx_check_nested_events handles it.
>>>>>     	 */
>>>>> -	if (is_guest_mode(vcpu) && nested_exit_on_intr(vcpu))
>>>>> +	if ((is_guest_mode(vcpu) && nested_exit_on_intr(vcpu)) || max_irr
>>>> ==
>>>>> +0)
>>
>> Its really not readable to modify max_irr as 0 and check that here, and
>> especially when you read the original comment.
>>
>> So what about this?
>
>
> I think both are ok.
> If we zero max_irr in vmx_set_rvi(), we still need this check:
> if ((is_guest_mode(vcpu) && nested_exit_on_intr(vcpu)) || max_irr == -1)

No, I don't think we need to add this.

>
> Let's see if Paolo has any comments, then send out a second version.
>
> Wei
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index
>> 0cd99d8..bc4558b 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -7280,6 +7280,9 @@ static void vmx_set_rvi(int vector)
>>           u16 status;
>>           u8 old;
>>
>> +       if (vector == -1)
>> +               vector = 0;
>> +
>>           status = vmcs_read16(GUEST_INTR_STATUS);
>>           old = (u8)status & 0xff;
>>           if ((u8)vector != old) {
>> @@ -7291,9 +7294,6 @@ static void vmx_set_rvi(int vector)
>>
>>    static void vmx_hwapic_irr_update(struct kvm_vcpu *vcpu, int max_irr)
>>    {
>> -       if (max_irr == -1)
>> -               return;
>> -
>>           /*
>>            * If a vmexit is needed, vmx_check_nested_events handles it.
>>            */
>> @@ -7305,6 +7305,9 @@ static void vmx_hwapic_irr_update(struct
>> kvm_vcpu *vcpu, int max_irr)
>>                   return;
>>           }
>>
>> +       if (max_irr == -1)
>> +               return;
>> +

Did you see this?

Tiejun

>>           /*
>>            * Fall back to pre-APICv interrupt injection since L2
>>            * is run without virtual interrupt delivery.
>>
>>
>> Thanks
>> Tiejun
>>
>>>>>     		return;
>>>>>
>>>>> -	if (!is_guest_mode(vcpu)) {
>>>>> -		vmx_set_rvi(max_irr);
>>>>> -		return;
>>>>> -	}
>>>>> -
>>>>>     	/*
>>>>>     	 * Fall back to pre-APICv interrupt injection since L2
>>>>>     	 * is run without virtual interrupt delivery.
>>>>>
>>>
>>>
>
>