Re: [PATCH 1/1] KVM: s390: diag9c forwarding

[Pierre Morel <pmorel@linux.ibm.com>]

On 1/19/21 5:53 PM, Cornelia Huck wrote:
> On Mon, 18 Jan 2021 14:17:39 +0100
> Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> 
>> From: Pierre Morel <pmorel@linux.ibm.com>
>>
>> When we receive intercept a DIAG_9C from the guest we verify
>> that the target real CPU associated with the virtual CPU
>> designated by the guest is running and if not we forward the
>> DIAG_9C to the target real CPU.
>>
>> To avoid a diag9c storm we allow a maximal rate of diag9c forwarding.
>>
>> The rate is calculated as a count per second defined as a
>> new parameter of the s390 kvm module: diag9c_forwarding_hz .
>>
>> The default value is to not forward diag9c.
>>
>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
>> ---
>>   arch/s390/include/asm/kvm_host.h |  1 +
>>   arch/s390/include/asm/smp.h      |  1 +
>>   arch/s390/kernel/smp.c           |  1 +
>>   arch/s390/kvm/diag.c             | 31 ++++++++++++++++++++++++++++---
>>   arch/s390/kvm/kvm-s390.c         |  6 ++++++
>>   arch/s390/kvm/kvm-s390.h         |  8 ++++++++
>>   6 files changed, 45 insertions(+), 3 deletions(-)
>>
> 
> (...)
> 
>> @@ -167,9 +180,21 @@ static int __diag_time_slice_end_directed(struct kvm_vcpu *vcpu)
>>   	if (!tcpu)
>>   		goto no_yield;
>>   
>> -	/* target already running */
>> -	if (READ_ONCE(tcpu->cpu) >= 0)
>> -		goto no_yield;
>> +	/* target VCPU already running */
> 
> Maybe make this /* target guest VPCU already running */...
> 
>> +	if (READ_ONCE(tcpu->cpu) >= 0) {
>> +		if (!diag9c_forwarding_hz || diag9c_forwarding_overrun())
>> +			goto no_yield;
>> +
>> +		/* target CPU already running */
> 
> ...and this /* target host CPU already running */? I just read this
> several times and was confused before I spotted the difference :)

I can only agree then :) .

...


-- 
Pierre Morel
IBM Lab Boeblingen