Re: [PATCH v10 2/3] KVM: s390: guest support for topology function

[Pierre Morel]

On 6/24/22 17:09, Janis Schoetterl-Glausch wrote:
> On 6/20/22 14:54, Pierre Morel wrote:
> > We report a topology change to the guest for any CPU hotplug.
> >
> > The reporting to the guest is done using the Multiprocessor
> > Topology-Change-Report (MTCR) bit of the utility entry in the guest's
> > SCA which will be cleared during the interpretation of PTF.
> >
> > On every vCPU creation we set the MCTR bit to let the guest know the
> > next time he uses the PTF with command 2 instruction that the
> > topology changed and that he should use the STSI(15.1.x) instruction
> > to get the topology details.
> >
> > STSI(15.1.x) gives information on the CPU configuration topology.
> > Let's accept the interception of STSI with the function code 15 and
> > let the userland part of the hypervisor handle it when userland
> > support the CPU Topology facility.
> >
> > Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
> > ---
> >   arch/s390/include/asm/kvm_host.h | 11 ++++++++---
> >   arch/s390/kvm/kvm-s390.c         | 27 ++++++++++++++++++++++++++-
> >   arch/s390/kvm/priv.c             | 15 +++++++++++----
> >   arch/s390/kvm/vsie.c             |  3 +++
> >   4 files changed, 48 insertions(+), 8 deletions(-)
> [...]
>
> > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> > index 8fcb56141689..95b96019ca8e 100644
> > --- a/arch/s390/kvm/kvm-s390.c
> > +++ b/arch/s390/kvm/kvm-s390.c
> > @@ -1691,6 +1691,25 @@ static int kvm_s390_get_cpu_model(struct kvm *kvm, struct kvm_device_attr *attr)
> >   	return ret;
> >   }
> >
> > +/**
> > + * kvm_s390_sca_set_mtcr
> > + * @kvm: guest KVM description
> > + *
> > + * Is only relevant if the topology facility is present,
> > + * the caller should check KVM facility 11
> > + *
> > + * Updates the Multiprocessor Topology-Change-Report to signal
> > + * the guest with a topology change.
> > + */
> > +static void kvm_s390_sca_set_mtcr(struct kvm *kvm)
> > +{
> > +	struct bsca_block *sca = kvm->arch.sca; /* SCA version doesn't matter */
> > +
> > +	ipte_lock(kvm);
>
> Why do we need to take the ipte lock here and in patch 3?

That is a good question.
I fear I was tired as I understood that from the documentation, after 
re-reading, we need an interlocked-update not an ipte lock update.
... I have to change that


> > +	sca->utility |= SCA_UTILITY_MTCR;
> > +	ipte_unlock(kvm);
> > +}
>
> [...]

--
Pierre Morel
IBM Lab Boeblingen