Re: [PATCH] KVM: s390: fix gisa destroy operation might lead to cpu stalls

[Michael Mueller <mimu@linux.ibm.com>]

On 23.08.23 15:23, Alexander Gordeev wrote:
> On Wed, Aug 23, 2023 at 02:41:40PM +0200, Michael Mueller wrote:
> ...
>> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
>> index 9bd0a873f3b1..73153bea6c24 100644
>> --- a/arch/s390/kvm/interrupt.c
>> +++ b/arch/s390/kvm/interrupt.c
>> @@ -3205,8 +3205,10 @@ void kvm_s390_gisa_destroy(struct kvm *kvm)
>>   	if (gi->alert.mask)
>>   		KVM_EVENT(3, "vm 0x%pK has unexpected iam 0x%02x",
>>   			  kvm, gi->alert.mask);
>> -	while (gisa_in_alert_list(gi->origin))
>> -		cpu_relax();
>> +	while (gisa_in_alert_list(gi->origin)) {
>> +		KVM_EVENT(3, "vm 0x%pK gisa in alert list during destroy", kvm);
>> +		process_gib_alert_list();
> 
> process_gib_alert_list() has two nested loops and neither of them
> does cpu_relax(). I guess, those are needed instead of one you remove?

Calling function process_gib_alert_list() guarantees the gisa
is taken out of the alert list immediately and thus the potential
endless loop on gisa_in_alert_list() is solved. The issue surfaced
with the following patch that accidently disabled the GAL interrupt
processing on the host that normaly handles the alert list.
The patch has been reverted from devel and will be re-applied in v2.

88a096a7a460 Revert "s390/airq: remove lsi_mask from airq_struct"
a9d17c5d8813 s390/airq: remove lsi_mask from airq_struct

Does that make sense for you?

> 
>> +	}
>>   	hrtimer_cancel(&gi->timer);
>>   	gi->origin = NULL;
>>   	VM_EVENT(kvm, 3, "gisa 0x%pK destroyed", gisa);