Re: [PATCH] KVM: arm/arm64: don't set vtimer->cnt_ctl in kvm_arch_timer_handler

[Auger Eric]

Marc,
On 13/12/17 09:56, Marc Zyngier wrote:
> Hi Jia,
> 
> On 13/12/17 07:00, Jia He wrote:
>> In our Armv8a server (qualcomm Amberwing, non VHE), after applying
>> Christoffer's timer optimizing patchset(Optimize arch timer register
>> handling), the guest is hang during kernel booting.
>>
>> The error root cause might be as follows:
>> 1. in kvm_arch_timer_handler, it reset vtimer->cnt_ctl with current
>> cntv_ctl register value. And then it missed some cases to update timer's
>> irq (irq.level) when kvm_timer_irq_can_fire() is false
>> 2. It causes kvm_vcpu_check_block return 0 instead of -EINTR
>> 	kvm_vcpu_check_block
>> 		kvm_cpu_has_pending_timer
>> 			kvm_timer_is_pending
>> 				kvm_timer_should_fire
>> 3. Thus, the kvm hyp code can not break the loop in kvm_vcpu_block (halt
>> poll process) and the guest is hang forever
>>
>> Fixes: b103cc3f10c0 ("KVM: arm/arm64: Avoid timer save/restore in vcpu entry/exit")
>> Signed-off-by: Jia He <jia.he@xxxxxxxxxxxxxxxx>
>> ---
>>  virt/kvm/arm/arch_timer.c | 1 -
>>  1 file changed, 1 deletion(-)
>>
>> diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
>> index f9555b1..bb86433 100644
>> --- a/virt/kvm/arm/arch_timer.c
>> +++ b/virt/kvm/arm/arch_timer.c
>> @@ -100,7 +100,6 @@ static irqreturn_t kvm_arch_timer_handler(int irq, void *dev_id)
>>  	vtimer = vcpu_vtimer(vcpu);
>>  
>>  	if (!vtimer->irq.level) {
>> -		vtimer->cnt_ctl = read_sysreg_el0(cntv_ctl);
>>  		if (kvm_timer_irq_can_fire(vtimer))
>>  			kvm_timer_update_irq(vcpu, true, vtimer);
>>  	}
>>
> 
> Which patches are you looking at? The current code in mainline looks
> like this:
> 
> 	vtimer = vcpu_vtimer(vcpu);
> 
> 	vtimer->cnt_ctl = read_sysreg_el0(cntv_ctl);
> 	if (kvm_timer_irq_can_fire(vtimer))
> 		kvm_timer_update_irq(vcpu, true, vtimer);
> 
> I'd suggest you use mainline and report if this doesn't work
the removal of if (!vtimer->irq.level) test happened in:
[PATCH v7 3/8] KVM: arm/arm64: Don't cache the timer IRQ level

which is not upstream.

Thanks

Eric
> 
> Thanks,
> 
> 	M.
>