Re: [PATCH v9 3/3] s390x: KVM: resetting the Topology-Change-Report

Claudio Imbrenda
2022-05-12T09:53:03Z

On Thu, 12 May 2022 11:31:18 +0200
David Hildenbrand <david@redhat.com> wrote:

> On 06.05.22 11:24, Pierre Morel wrote:
> > During a subsystem reset the Topology-Change-Report is cleared.
> > Let's give userland the possibility to clear the MTCR in the case
> > of a subsystem reset.
> >
> > To migrate the MTCR, let's give userland the possibility to
> > query the MTCR state.
> >
> > Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> > ---
> > arch/s390/include/uapi/asm/kvm.h | 5 ++
> > arch/s390/kvm/kvm-s390.c | 79 ++++++++++++++++++++++++++++++++
> > 2 files changed, 84 insertions(+)
> >
> > diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h
> > index 7a6b14874d65..abdcf4069343 100644
> > --- a/arch/s390/include/uapi/asm/kvm.h
> > +++ b/arch/s390/include/uapi/asm/kvm.h
> > @@ -74,6 +74,7 @@ struct kvm_s390_io_adapter_req {
> > #define KVM_S390_VM_CRYPTO 2
> > #define KVM_S390_VM_CPU_MODEL 3
> > #define KVM_S390_VM_MIGRATION 4
> > +#define KVM_S390_VM_CPU_TOPOLOGY 5
> >
> > /* kvm attributes for mem_ctrl */
> > #define KVM_S390_VM_MEM_ENABLE_CMMA 0
> > @@ -171,6 +172,10 @@ struct kvm_s390_vm_cpu_subfunc {
> > #define KVM_S390_VM_MIGRATION_START 1
> > #define KVM_S390_VM_MIGRATION_STATUS 2
> >
> > +/* kvm attributes for cpu topology */
> > +#define KVM_S390_VM_CPU_TOPO_MTR_CLEAR 0
> > +#define KVM_S390_VM_CPU_TOPO_MTR_SET 1
> > +
> > /* for KVM_GET_REGS and KVM_SET_REGS */
> > struct kvm_regs {
> > /* general purpose regs for s390 */
> > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> > index c8bdce31464f..80a1244f0ead 100644
> > --- a/arch/s390/kvm/kvm-s390.c
> > +++ b/arch/s390/kvm/kvm-s390.c
> > @@ -1731,6 +1731,76 @@ static void kvm_s390_sca_set_mtcr(struct kvm *kvm)
> > ipte_unlock(kvm);
> > }
> >
> > +/**
> > + * kvm_s390_sca_clear_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_clear_mtcr(struct kvm *kvm)
> > +{
> > + struct bsca_block *sca = kvm->arch.sca; /* SCA version doesn't matter */
> > +
> > + ipte_lock(kvm);
> > + sca->utility &= ~SCA_UTILITY_MTCR;
>
>
> One space too much.
>
> sca->utility &= ~SCA_UTILITY_MTCR;
>
> > + ipte_unlock(kvm);
> > +}
> > +
> > +static int kvm_s390_set_topology(struct kvm *kvm, struct kvm_device_attr *attr)
> > +{
> > + if (!test_kvm_facility(kvm, 11))
> > + return -ENXIO;
> > +
> > + switch (attr->attr) {
> > + case KVM_S390_VM_CPU_TOPO_MTR_SET:
> > + kvm_s390_sca_set_mtcr(kvm);
> > + break;
> > + case KVM_S390_VM_CPU_TOPO_MTR_CLEAR:
> > + kvm_s390_sca_clear_mtcr(kvm);
> > + break;
> > + }
> > + return 0;
> > +}
> > +
> > +/**
> > + * kvm_s390_sca_get_mtcr
> > + * @kvm: guest KVM description
> > + *
> > + * Is only relevant if the topology facility is present,
> > + * the caller should check KVM facility 11
> > + *
> > + * reports to QEMU the Multiprocessor Topology-Change-Report.
> > + */
> > +static int kvm_s390_sca_get_mtcr(struct kvm *kvm)
> > +{
> > + struct bsca_block *sca = kvm->arch.sca; /* SCA version doesn't matter */
> > + int val;
> > +
> > + ipte_lock(kvm);
> > + val = !!(sca->utility & SCA_UTILITY_MTCR);
> > + ipte_unlock(kvm);
> > +
> > + return val;
> > +}
> > +
> > +static int kvm_s390_get_topology(struct kvm *kvm, struct kvm_device_attr *attr)
> > +{
> > + int mtcr;
>
> I think we prefer something like u16 when copying to user space.

but then userspace also has to expect a u16, right?

>
> > +
> > + if (!test_kvm_facility(kvm, 11))
> > + return -ENXIO;
> > +
> > + mtcr = kvm_s390_sca_get_mtcr(kvm);
> > + if (copy_to_user((void __user *)attr->addr, &mtcr, sizeof(mtcr)))
> > + return -EFAULT;
> > +
> > + return 0;
> > +}
>
> You should probably add documentation, and document that only the last
> bit (0x1) has a meaning.
>
> Apart from that LGTM.
>