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

David Hildenbrand
2022-05-12T09:31:30Z

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.

> +
> + 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.

--
Thanks,

David / dhildenb