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Subject: Re: [PATCH] KVM: s390x: add debug statement for diag 318 CPNC data
To:     Collin Walling <walling@linux.ibm.com>, linux-s390@vger.kernel.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc:     frankja@linux.ibm.com, david@redhat.com, imbrenda@linux.ibm.com
References: <20211027025451.290124-1-walling@linux.ibm.com>
From:   Christian Borntraeger <borntraeger@de.ibm.com>
Message-ID: <ab36ddd3-1a05-ec6a-3c6e-a8881956d0e2@de.ibm.com>
Date:   Wed, 27 Oct 2021 07:37:06 +0200
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Am 27.10.21 um 04:54 schrieb Collin Walling:
> 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@linux.ibm.com>

Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>

And it even finds a bug in QEMU. We clear the CPNC on local CPU resets.
Can you have a look? I think we just have to move the cpnc in the env
field from the normal/initial reset range to the full reset range.
> ---
>   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,
>