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

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

On 5/24/22 13:27, Thomas Huth wrote:
> 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 ?

Should have historical reason I forgot in between.
I will move it in 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_has390_handle_ptfndle_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?

OK, I will have a look and change it.

Thanks,
Pierre

> 
>   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;
> 

-- 
Pierre Morel
IBM Lab Boeblingen