Re: [PATCH v3 2/4] s390x: kvm: topology: interception of PTF instruction

[Thomas Huth]

On 16/09/2021 15.50, 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         | 36 ++++++++++++++++++++++++++++++
>   include/hw/s390x/s390-virtio-ccw.h |  6 +++++
>   target/s390x/kvm/kvm.c             | 15 +++++++++++++
>   3 files changed, 57 insertions(+)
>
> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> index 61aeccb163..894f013139 100644
> --- a/hw/s390x/s390-virtio-ccw.c
> +++ b/hw/s390x/s390-virtio-ccw.c
> @@ -404,6 +404,42 @@ static void s390_pv_prepare_reset(S390CcwMachineState *ms)
>       s390_pv_prep_reset();
>   }
>   

Could you please add a comment in front of this function, with some 
explanations? If I've got that right, it's currently rather only a "dummy" 
function, rejecting FC 0 and 1, and FC 2 is always handled by the SIE, right?

> +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 5b1fdb55c4..dd036961fe 100644
> --- a/target/s390x/kvm/kvm.c
> +++ b/target/s390x/kvm/kvm.c
> @@ -97,6 +97,7 @@
>   
>   #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
> @@ -362,6 +363,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>       kvm_vm_enable_cap(s, KVM_CAP_S390_USER_SIGP, 0);
>       kvm_vm_enable_cap(s, KVM_CAP_S390_VECTOR_REGISTERS, 0);
>       kvm_vm_enable_cap(s, KVM_CAP_S390_USER_STSI, 0);
> +    kvm_vm_enable_cap(s, KVM_CAP_S390_CPU_TOPOLOGY, 0);

Should this maybe rather be done in the last patch, to avoid a state where 
PTF is available, but STSI 15 is not implemented yet (when bisecting through 
these commits later)?

 Thomas