Re: kernel device reset support

Dong, Eddie
2007-10-09T10:11:49Z

Avi Kivity wrote:
>> In native, RESET signal force every processor enter "RESET" status,
>> and then immediately after RESET signal is removed, all CPUs will
>> compete for BSP role, the winner continue execution, and failor will
>> be blocked till INIT/SIPI/SIPI.
>>
>
> I meant, you could set both to VCPU_MP_STATE_UNINITIALIZED and let the
> vcpu code do the reset differently depending on vcpu_id. This way you
> don't run into locking issues (kvm_lapic_reset() needs the vcpu lock?)

If BSP mp_state becomes VCPU_MP_STATE_UNINITIALIZED, current code
can't wakeup it. We need additional code that I am not aware of now.

Current VCPU must be BSP, otherwise the code executing in Qemu will have
problem too.

>> For a graceful reboot, this one is not needed since every APs are
>> already brought to HALT status before BSP issue RESET signal. But in
>> case of non-graceful reboot, it is possible the VCPUs are still
>> executing guest instruction, so we kick the VCPU and then use this
>> logic to force the exception handler to be a heavy VM Exit and
>> execute following code at beginning of kvm_vcpu_ioctl_run. (Let
>> VCPU_MP_STATE_UNINITIALIZED take effective)
>>
>> if (unlikely(vcpu->mp_state ==
> VCPU_MP_STATE_UNINITIALIZED)) {
>> if (irqchip_in_kernel(vcpu->kvm) && vcpu->apic)
>> kvm_lapic_reset(vcpu);
>> kvm_vcpu_block(vcpu);
>> vcpu_put(vcpu);
>> return -EAGAIN;
>> }
>>
>> Whether we need to handle those un-graceful reboot case is up to you
>> :-) If not, then those code can be removed.
>>
>
> We do need to support ungraceful resets. But this could
> easily be done
> via vcpu->requests.

Mmm, almost Yes, then it is same with force_to_quit.
But reset doesn't mean lapic_reset only, it needs to
enter wait for INIT/SIPI cycles. So using mp_state is
much closer.

>
> To reset a vcpu:
>
> set_bit(KVM_REQ_RESET, &vcpu->requests)
> kvm_vcpu_kick(vcpu);
>
> And in __vcpu_run():
>
> if (vcpu_requests) {
> if (test_and_reset_bit(KVM_REQ_RESET, &vcpu->requests))
> .... }
>
>>
>> Mmm, I will move this to be after VCPU reset.
>> If a VCPU is still accessing (write) devices register, we always
>> have problem. So move after all the processors enetring frozen state
>> will be simple and safer.
>>
>> Any opnion? Will post after your new comments.
>>
>>
>
> Sounds good. But the BSP starts executing immediately, no?

Yes, BSP will continue. current VCPU=BSP.

>
> So maybe two stages for vcpu reset: first to reset and halt it, then
> start it. pic and ioapic reset can be performed in between.
>
thx,eddie