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

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Message-ID: <4488b572-11bf-72ff-86c0-395dfc7b3f71@linux.ibm.com>
Date:   Mon, 8 Nov 2021 12:12:13 +0100
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     Collin Walling <walling@...ux.ibm.com>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     borntraeger@...ibm.com, david@...hat.com, imbrenda@...ux.ibm.com
Subject: Re: [PATCH] KVM: s390x: add debug statement for diag 318 CPNC data

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?