Re: [PATCH v7 10/13] s390x: kvm: topology: interception of PTF instruction

[Thomas Huth <thuth@redhat.com>]

On 20/04/2022 13.57, 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.
> 
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
>   hw/s390x/s390-virtio-ccw.c         | 50 ++++++++++++++++++++++++++++++
>   include/hw/s390x/s390-virtio-ccw.h |  6 ++++
>   target/s390x/kvm/kvm.c             | 14 +++++++++
>   3 files changed, 70 insertions(+)
> 
> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> index 93d1a43583..1ffaddebcc 100644
> --- a/hw/s390x/s390-virtio-ccw.c
> +++ b/hw/s390x/s390-virtio-ccw.c

Why do you put this into s390-virtio-ccw.c and not into cpu_topology.c ?

> @@ -434,6 +434,56 @@ static void s390_pv_prepare_reset(S390CcwMachineState *ms)
>       s390_pv_prep_reset();
>   }
>   
> +/*
> + * 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.
> + *
> + * Function code 2 is handling topology changes and is interpreted
> + * by the SIE.
> + */
> +int 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 0;
> +    }
> +
> +    if (env->psw.mask & PSW_MASK_PSTATE) {
> +        s390_program_interrupt(env, PGM_PRIVILEGED, ra);
> +        return 0;
> +    }
> +
> +    if (reg & ~S390_TOPO_FC_MASK) {
> +        s390_program_interrupt(env, PGM_SPECIFICATION, ra);
> +        return 0;
> +    }
> +
> +    switch (fc) {
> +    case 0:    /* Horizontal polarization is already set */
> +        env->regs[r1] |= S390_PTF_REASON_DONE;
> +        return 2;
> +    case 1:    /* Vertical polarization is not supported */
> +        env->regs[r1] |= S390_PTF_REASON_NONE;
> +        return 2;
> +    default:
> +        /* Note that fc == 2 is interpreted by the SIE */
> +        s390_program_interrupt(env, PGM_SPECIFICATION, ra);
> +    }
> +
> +    return 0;
> +}
> +
>   static void s390_machine_reset(MachineState *machine)
>   {
>       S390CcwMachineState *ms = S390_CCW_MACHINE(machine);
> diff --git a/include/hw/s390x/s390-virtio-ccw.h b/include/hw/s390x/s390-virtio-ccw.h
> index 3331990e02..ac4b4a92e7 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
> +int s390_handle_ptf(S390CPU *cpu, uint8_t r1, uintptr_t ra);
> +
>   struct S390CcwMachineClass {
>       /*< private >*/
>       MachineClass parent_class;
> diff --git a/target/s390x/kvm/kvm.c b/target/s390x/kvm/kvm.c
> index 27b3fbfa09..e3792e52c2 100644
> --- a/target/s390x/kvm/kvm.c
> +++ b/target/s390x/kvm/kvm.c
> @@ -98,6 +98,7 @@
>   
>   #define PRIV_B9_EQBS                    0x9c
>   #define PRIV_B9_CLP                     0xa0
> +#define PRIV_B9_PTF                     0xa2
>   #define PRIV_B9_PCISTG                  0xd0
>   #define PRIV_B9_PCILG                   0xd2
>   #define PRIV_B9_RPCIT                   0xd3
> @@ -1453,6 +1454,16 @@ static int kvm_mpcifc_service_call(S390CPU *cpu, struct kvm_run *run)
>       }
>   }
>   
> +static int kvm_handle_ptf(S390CPU *cpu, struct kvm_run *run)
> +{
> +    uint8_t r1 = (run->s390_sieic.ipb >> 20) & 0x0f;
> +    int ret;
> +
> +    ret = s390_handle_ptf(cpu, r1, RA_IGNORED);
> +    setcc(cpu, ret);

So you're still setting the CC in case the s390_handle_ptf() function 
injected a program interrupt? ... feels wrong. Maybe the CC should be set 
within s390_handle_ptf() instead?

  Thomas


> +    return 0;
> +}
> +
>   static int handle_b9(S390CPU *cpu, struct kvm_run *run, uint8_t ipa1)
>   {
>       int r = 0;
> @@ -1470,6 +1481,9 @@ static int handle_b9(S390CPU *cpu, struct kvm_run *run, uint8_t ipa1)
>       case PRIV_B9_RPCIT:
>           r = kvm_rpcit_service_call(cpu, run);
>           break;
> +    case PRIV_B9_PTF:
> +        r = kvm_handle_ptf(cpu, run);
> +        break;
>       case PRIV_B9_EQBS:
>           /* just inject exception */
>           r = -1;