Re: [PATCH v14 06/11] s390x/cpu topology: interception of PTF instruction

[Nina Schoetterl-Glausch]

On Thu, 2023-01-05 at 15:53 +0100, Pierre Morel wrote:
> When the host supports the CPU topology facility, the PTF
> instruction with function code 2 is interpreted by the SIE,
> provided that the userland hypervizor activates the interpretation
> by using the KVM_CAP_S390_CPU_TOPOLOGY KVM extension.
> 
> The PTF instructions with function code 0 and 1 are intercepted
> and must be emulated by the userland hypervizor.
> 
> During RESET all CPU of the configuration are placed in
> horizontal polarity.
> 
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
>  include/hw/s390x/cpu-topology.h    |  3 +
>  include/hw/s390x/s390-virtio-ccw.h |  6 ++
>  target/s390x/cpu.h                 |  1 +
>  hw/s390x/cpu-topology.c            | 92 ++++++++++++++++++++++++++++++
>  target/s390x/cpu-sysemu.c          | 16 ++++++
>  target/s390x/kvm/kvm.c             | 11 ++++
>  6 files changed, 129 insertions(+)
> 
> diff --git a/include/hw/s390x/cpu-topology.h b/include/hw/s390x/cpu-topology.h
> index 9571aa70e5..33e23d78b9 100644
> --- a/include/hw/s390x/cpu-topology.h
> +++ b/include/hw/s390x/cpu-topology.h
> @@ -55,11 +55,13 @@ typedef struct S390Topology {
>      QTAILQ_HEAD(, S390TopologyEntry) list;
>      uint8_t *sockets;
>      CpuTopology *smp;
> +    int polarity;
>  } S390Topology;
>  
>  #ifdef CONFIG_KVM
>  bool s390_has_topology(void);
>  void s390_topology_set_cpu(MachineState *ms, S390CPU *cpu, Error **errp);
> +void s390_topology_set_polarity(int polarity);
>  #else
>  static inline bool s390_has_topology(void)
>  {
> @@ -68,6 +70,7 @@ static inline bool s390_has_topology(void)
>  static inline void s390_topology_set_cpu(MachineState *ms,
>                                           S390CPU *cpu,
>                                           Error **errp) {}
> +static inline void s390_topology_set_polarity(int polarity) {}
>  #endif
>  extern S390Topology s390_topology;
>  
> diff --git a/include/hw/s390x/s390-virtio-ccw.h 
> b/include/hw/s390x/s390-virtio-ccw.h
> index 9bba21a916..c1d46e78af 100644
> --- a/include/hw/s390x/s390-virtio-ccw.h
> +++ b/include/hw/s390x/s390-virtio-ccw.h
> @@ -30,6 +30,12 @@ struct S390CcwMachineState {
>      uint8_t loadparm[8];
>  };
>  
> +#define S390_PTF_REASON_NONE (0x00 << 8)
> +#define S390_PTF_REASON_DONE (0x01 << 8)
> +#define S390_PTF_REASON_BUSY (0x02 << 8)
> +#define S390_TOPO_FC_MASK 0xffUL
> +void s390_handle_ptf(S390CPU *cpu, uint8_t r1, uintptr_t ra);
> +
>  struct S390CcwMachineClass {
>      /*< private >*/
>      MachineClass parent_class;
> diff --git a/target/s390x/cpu.h b/target/s390x/cpu.h
> index 01ade07009..5da4041576 100644
> --- a/target/s390x/cpu.h
> +++ b/target/s390x/cpu.h
> @@ -864,6 +864,7 @@ void s390_do_cpu_set_diag318(CPUState *cs, 
> run_on_cpu_data arg);
>  int s390_assign_subch_ioeventfd(EventNotifier *notifier, uint32_t sch_id,
>                                  int vq, bool assign);
>  void s390_cpu_topology_reset(void);
> +void s390_cpu_topology_set(void);

I don't like this name much, it's nondescript.
s390_cpu_topology_set_modified ?

>  #ifndef CONFIG_USER_ONLY
>  unsigned int s390_cpu_set_state(uint8_t cpu_state, S390CPU *cpu);
>  #else
> diff --git a/hw/s390x/cpu-topology.c b/hw/s390x/cpu-topology.c
> index 438055c612..e6b4692581 100644
> --- a/hw/s390x/cpu-topology.c
> +++ b/hw/s390x/cpu-topology.c
> @@ -97,6 +97,98 @@ static s390_topology_id s390_topology_from_cpu(S390CPU 
> *cpu)
>  }
>  
>  /**
> + * s390_topology_set_polarity
> + * @polarity: horizontal or vertical
> + *
> + * Changes the polarity of all the CPU in the configuration.
> + *
> + * If the dedicated CPU modifier attribute is set a vertical
> + * polarization is always high (Architecture).
> + * Otherwise we decide to set it as medium.
> + *
> + * Once done, advertise a topology change.
> + */
> +void s390_topology_set_polarity(int polarity)

I don't like that this function ignores what kind of vertical polarization is 
passed,
it's confusing.
That seems like a further reason to split horizontal/vertical from the 
entitlement.

> +{
> +    S390TopologyEntry *entry;

I also expected this function to set s390_topology.polarization, but it doesn't.
> +
> +    QTAILQ_FOREACH(entry, &s390_topology.list, next) {
> +        if (polarity == S390_TOPOLOGY_POLARITY_HORIZONTAL) {
> +            entry->id.p = polarity;
> +        } else {
> +            if (entry->id.d) {
> +                entry->id.p = S390_TOPOLOGY_POLARITY_VERTICAL_HIGH;
> +            } else {
> +                entry->id.p = S390_TOPOLOGY_POLARITY_VERTICAL_MEDIUM;
> +            }
> +        }
> +    }
> +    s390_cpu_topology_set();
> +}
> +
> +/*
> + * s390_handle_ptf:
> + *
> + * @register 1: contains the function code
> + *
> + * Function codes 0 and 1 handle the CPU polarization.
> + * We assume an horizontal topology, the only one supported currently
> + * by Linux, consequently we answer to function code 0, requesting
> + * horizontal polarization that it is already the current polarization
> + * and reject vertical polarization request without further explanation.

This comment is outdated, right? Same for those in the function body.

> + *
> + * Function code 2 is handling topology changes and is interpreted
> + * by the SIE.
> + */
> +void s390_handle_ptf(S390CPU *cpu, uint8_t r1, uintptr_t ra)
> +{
> +    CPUS390XState *env = &cpu->env;
> +    uint64_t reg = env->regs[r1];
> +    uint8_t fc = reg & S390_TOPO_FC_MASK;
> +
> +    if (!s390_has_feat(S390_FEAT_CONFIGURATION_TOPOLOGY)) {
> +        s390_program_interrupt(env, PGM_OPERATION, ra);
> +        return;
> +    }
> +
> +    if (env->psw.mask & PSW_MASK_PSTATE) {
> +        s390_program_interrupt(env, PGM_PRIVILEGED, ra);
> +        return;
> +    }
> +
> +    if (reg & ~S390_TOPO_FC_MASK) {
> +        s390_program_interrupt(env, PGM_SPECIFICATION, ra);
> +        return;
> +    }
> +
> +    switch (fc) {
> +    case 0:    /* Horizontal polarization is already set */
> +        if (s390_topology.polarity == S390_TOPOLOGY_POLARITY_HORIZONTAL) {
> +            env->regs[r1] |= S390_PTF_REASON_DONE;
> +            setcc(cpu, 2);
> +        } else {
> +            s390_topology_set_polarity(S390_TOPOLOGY_POLARITY_HORIZONTAL);
> +            s390_topology.polarity = S390_TOPOLOGY_POLARITY_HORIZONTAL;
> +            setcc(cpu, 0);
> +        }
> +        break;
> +    case 1:    /* Vertical polarization is not supported */
> +        if (s390_topology.polarity != S390_TOPOLOGY_POLARITY_HORIZONTAL) {
> +            env->regs[r1] |= S390_PTF_REASON_DONE;
> +            setcc(cpu, 2);
> +        } else {
> +            s390_topology_set_polarity(S390_TOPOLOGY_POLARITY_VERTICAL_LOW);

This is why I said it's confusing, nothing gets set to LOW.

> +            s390_topology.polarity = S390_TOPOLOGY_POLARITY_VERTICAL_LOW;

Why LOW here?

> +            setcc(cpu, 0);
> +        }
> +        break;
> +    default:
> +        /* Note that fc == 2 is interpreted by the SIE */
> +        s390_program_interrupt(env, PGM_SPECIFICATION, ra);
> +    }

You can simplify this by doing:

int new_polarity;
switch (fc) {
case 0:
        new_polarity = S390_TOPOLOGY_POLARITY_HORIZONTAL;
        break;
case 1:
        new_polarity = S390_TOPOLOGY_POLARITY_VERTICAL_?;
        break;
default:
        /* Note that fc == 2 is interpreted by the SIE */
        s390_program_interrupt(env, PGM_SPECIFICATION, ra);
        return;
}

if same polarity:
        rc done, rejected
else
        set polarity, initiated

Might be a good idea to turn the polarity values into an enum.

> +}
[...]