linux-kernel - Re: [PATCH] KVM: s390x: add debug statement for diag 318 CPNC data

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Message-ID: <28d90d6f-b481-3588-cd33-39624710b7bd@de.ibm.com>
Date:   Mon, 8 Nov 2021 13:04:14 +0100
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Janosch Frank <frankja@...ux.ibm.com>,
        Collin Walling <walling@...ux.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     david@...hat.com, imbrenda@...ux.ibm.com
Subject: Re: [PATCH] KVM: s390x: add debug statement for diag 318 CPNC data



Am 08.11.21 um 12:12 schrieb Janosch Frank:
> On 10/27/21 04:54, Collin Walling wrote:
>> The diag 318 data contains values that denote information regarding the
>> guest's environment. Currently, it is unecessarily difficult to observe
>> this value (either manually-inserted debug statements, gdb stepping, mem
>> dumping etc). It's useful to observe this information to obtain an
>> at-a-glance view of the guest's environment, so lets add a simple VCPU
>> event that prints the CPNC to the s390dbf logs.
>>
>> Signed-off-by: Collin Walling <walling@...ux.ibm.com>
>> ---
>>   arch/s390/kvm/kvm-s390.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index 6a6dd5e1daf6..da3ff24eabd0 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -4254,6 +4254,7 @@ static void sync_regs_fmt2(struct kvm_vcpu *vcpu)
>>       if (kvm_run->kvm_dirty_regs & KVM_SYNC_DIAG318) {
>>           vcpu->arch.diag318_info.val = kvm_run->s.regs.diag318;
>>           vcpu->arch.sie_block->cpnc = vcpu->arch.diag318_info.cpnc;
>> +        VCPU_EVENT(vcpu, 2, "setting cpnc to %d", vcpu->arch.diag318_info.cpnc);
>>       }
>>       /*
>>        * If userspace sets the riccb (e.g. after migration) to a valid state,
>>
> 
> Won't that turn up for every vcpu and spam the log?

only if the userspace always sets the dirty bit (which it should not).