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

[Christian Borntraeger]

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@xxxxxxxxxxxxx>
> > ---
> >   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).