Re: [PATCH v15 05/11] s390x/cpu topology: resetting the Topology-Change-Report

[Nina Schoetterl-Glausch <nsg@linux.ibm.com>]

On Wed, 2023-02-01 at 14:20 +0100, Pierre Morel wrote:
> During a subsystem reset the Topology-Change-Report is cleared
> by the machine.
> Let's ask KVM to clear the Modified Topology Change Report (MTCR)
> bit of the SCA in the case of a subsystem reset.
> 
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
>  include/hw/s390x/cpu-topology.h |  1 +
>  target/s390x/cpu.h              |  1 +
>  target/s390x/kvm/kvm_s390x.h    |  1 +
>  hw/s390x/cpu-topology.c         | 12 ++++++++++++
>  hw/s390x/s390-virtio-ccw.c      |  3 +++
>  target/s390x/cpu-sysemu.c       | 13 +++++++++++++
>  target/s390x/kvm/kvm.c          | 17 +++++++++++++++++
>  7 files changed, 48 insertions(+)
> 
> diff --git a/include/hw/s390x/cpu-topology.h b/include/hw/s390x/cpu-topology.h
> index 1ae7e7c5e3..60e0b9fbfa 100644
> --- a/include/hw/s390x/cpu-topology.h
> +++ b/include/hw/s390x/cpu-topology.h
> @@ -66,5 +66,6 @@ static inline void s390_topology_set_cpu(MachineState *ms,
>  
>  extern S390Topology s390_topology;
>  int s390_socket_nb(S390CPU *cpu);
> +void s390_topology_reset(void);
>  
>  #endif
> diff --git a/target/s390x/cpu.h b/target/s390x/cpu.h
> index e1f6925856..848314d2a9 100644
> --- a/target/s390x/cpu.h
> +++ b/target/s390x/cpu.h
> @@ -641,6 +641,7 @@ typedef struct SysIBTl_cpu {
>  QEMU_BUILD_BUG_ON(sizeof(SysIBTl_cpu) != 16);
>  
>  void insert_stsi_15_1_x(S390CPU *cpu, int sel2, __u64 addr, uint8_t ar);
> +void s390_cpu_topology_reset(void);

How about you call this s390_cpu_topology_reset_modified, so it's symmetric
with the function you define in the next patch. You could also drop the "cpu"
from the name.

Or maybe even better, you only define a function for setting the modified state,
but make it take a bool argument. This way you also get rid of some code duplication
and it wouldn't harm readability IMO.

>  
>  /* MMU defines */
>  #define ASCE_ORIGIN           (~0xfffULL) /* segment table origin             */
> diff --git a/target/s390x/kvm/kvm_s390x.h b/target/s390x/kvm/kvm_s390x.h
> index f9785564d0..649dae5948 100644
> --- a/target/s390x/kvm/kvm_s390x.h
> +++ b/target/s390x/kvm/kvm_s390x.h
> @@ -47,5 +47,6 @@ void kvm_s390_crypto_reset(void);
>  void kvm_s390_restart_interrupt(S390CPU *cpu);
>  void kvm_s390_stop_interrupt(S390CPU *cpu);
>  void kvm_s390_set_diag318(CPUState *cs, uint64_t diag318_info);
> +int kvm_s390_topology_set_mtcr(uint64_t attr);
>  
>  #endif /* KVM_S390X_H */
> diff --git a/hw/s390x/cpu-topology.c b/hw/s390x/cpu-topology.c
> index a80a1ebf22..cf63f3dd01 100644
> --- a/hw/s390x/cpu-topology.c
> +++ b/hw/s390x/cpu-topology.c
> @@ -85,6 +85,18 @@ static void s390_topology_init(MachineState *ms)
>      QTAILQ_INSERT_HEAD(&s390_topology.list, entry, next);
>  }
>  
> +/**
> + * s390_topology_reset:
> + *
> + * Generic reset for CPU topology, calls s390_topology_reset()
> + * s390_topology_reset() to reset the kernel Modified Topology
> + * change record.
> + */
> +void s390_topology_reset(void)
> +{

I'm wondering if you shouldn't move the reset changes you do in the next patch
into this one. I don't see what they have to do with PTF emulation.

> +    s390_cpu_topology_reset();
> +}
> +
>  /**
>   * s390_topology_cpu_default:
>   * @cpu: pointer to a S390CPU
> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> index 9bc51a83f4..30fdfe41fa 100644
> --- a/hw/s390x/s390-virtio-ccw.c
> +++ b/hw/s390x/s390-virtio-ccw.c
> @@ -122,6 +122,9 @@ static void subsystem_reset(void)
>              device_cold_reset(dev);
>          }
>      }
> +    if (s390_has_topology()) {
> +        s390_topology_reset();
> +    }
>  }
>  
>  static int virtio_ccw_hcall_notify(const uint64_t *args)
> diff --git a/target/s390x/cpu-sysemu.c b/target/s390x/cpu-sysemu.c
> index 948e4bd3e0..e27864c5f5 100644
> --- a/target/s390x/cpu-sysemu.c
> +++ b/target/s390x/cpu-sysemu.c
> @@ -306,3 +306,16 @@ void s390_do_cpu_set_diag318(CPUState *cs, run_on_cpu_data arg)
>          kvm_s390_set_diag318(cs, arg.host_ulong);
>      }
>  }
> +
> +void s390_cpu_topology_reset(void)
> +{
> +    int ret;
> +
> +    if (kvm_enabled()) {
> +        ret = kvm_s390_topology_set_mtcr(0);
> +        if (ret) {
> +            error_report("Failed to set Modified Topology Change Report: %s",
> +                         strerror(-ret));
> +        }
> +    }
> +}
> diff --git a/target/s390x/kvm/kvm.c b/target/s390x/kvm/kvm.c
> index 5ea358cbb0..bc953151ce 100644
> --- a/target/s390x/kvm/kvm.c
> +++ b/target/s390x/kvm/kvm.c
> @@ -2592,6 +2592,23 @@ int kvm_s390_get_zpci_op(void)
>      return cap_zpci_op;
>  }
>  
> +int kvm_s390_topology_set_mtcr(uint64_t attr)
> +{
> +    struct kvm_device_attr attribute = {
> +        .group = KVM_S390_VM_CPU_TOPOLOGY,
> +        .attr  = attr,
> +    };
> +
> +    if (!s390_has_feat(S390_FEAT_CONFIGURATION_TOPOLOGY)) {
> +        return 0;
> +    }
> +    if (!kvm_vm_check_attr(kvm_state, KVM_S390_VM_CPU_TOPOLOGY, attr)) {
> +        return -ENOTSUP;
> +    }
> +
> +    return kvm_vm_ioctl(kvm_state, KVM_SET_DEVICE_ATTR, &attribute);
> +}
> +
>  void kvm_arch_accel_class_init(ObjectClass *oc)
>  {
>  }