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

[Pierre Morel <pmorel@linux.ibm.com>]

On 10/13/21 09:25, Thomas Huth wrote:
> 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
> 

Yes you are right, thanks.
Pierre

-- 
Pierre Morel
IBM Lab Boeblingen