Re: [PATCH v2 07/13] s390x: protvirt: SCLP interpretation

[Janosch Frank <frankja@linux.ibm.com>]

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On 11/29/19 11:43 AM, David Hildenbrand wrote:
> On 29.11.19 10:48, Janosch Frank wrote:
>> SCLP for a protected guest is done over the SIDAD, so we need to use
>> the s390_cpu_virt_mem_* functions to access the SIDAD instead of guest
>> memory when reading/writing SCBs.
> 
> ... Can you elaborate a bit more how that is going to be used? Did you
> hack in special memory access to something called "SIDAD" via
> s390_cpu_virt_mem_*?

For secure guests we can't ever access virtual guest memory, since we
have no access to the guest translation tables.

Hence we have the satellite block (SIDA) as a bounce buffer. SIE will
bounce referenced blocks of data (like the SCCB) over the SIDA.

The virt_mem functions go through the KVM mem op API. A KVM patch
reroutes mem op access to the SIDA. The alternative would be to map the
SIDA into vcpu_run.

> 
> I'd suggest a different access path ... especially because
> 
> a) it's confusing

Granted, there's a lot of inherent knowledge behind these patches.
And looking at my past answers to the KVM intercept patch I already
forgot lots of it.

> b) it's unclear how exceptions apply

There are no PGM exceptions, as they are pre-checked and reported by
SIE. There are however errors that the mem op API can return.

> 
> ...
> 
>>
>> To not confuse the sclp emulation, we set 0x4000 as the SCCB address,
>> since the function that injects the sclp external interrupt would
>> reject a zero sccb address.
>>
>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>> ---
>>  hw/s390x/sclp.c         | 17 +++++++++++++++++
>>  include/hw/s390x/sclp.h |  2 ++
>>  target/s390x/kvm.c      |  5 +++++
>>  3 files changed, 24 insertions(+)
>>
>> diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
>> index f57ce7b739..ca71ace664 100644
>> --- a/hw/s390x/sclp.c
>> +++ b/hw/s390x/sclp.c
>> @@ -193,6 +193,23 @@ static void sclp_execute(SCLPDevice *sclp, SCCB *sccb, uint32_t code)
>>      }
>>  }
>>  
>> +#define SCLP_PV_DUMMY_ADDR 0x4000
>> +int sclp_service_call_protected(CPUS390XState *env, uint64_t sccb,
>> +                                uint32_t code)
>> +{
>> +    SCLPDevice *sclp = get_sclp_device();
>> +    SCLPDeviceClass *sclp_c = SCLP_GET_CLASS(sclp);
>> +    SCCB work_sccb;
>> +    hwaddr sccb_len = sizeof(SCCB);
>> +
>> +    s390_cpu_virt_mem_read(env_archcpu(env), 0, 0, &work_sccb, sccb_len);
>> +    sclp_c->execute(sclp, &work_sccb, code);
>> +    s390_cpu_virt_mem_write(env_archcpu(env), 0, 0, &work_sccb,
>> +                            be16_to_cpu(work_sccb.h.length));
> 
> this access itself without handling exceptions looks dangerous as it is
> completely unclear what's happening here.

See above

> 
>> +    sclp_c->service_interrupt(sclp, SCLP_PV_DUMMY_ADDR);
>> +    return 0;
>> +}
>> +
>>  int sclp_service_call(CPUS390XState *env, uint64_t sccb, uint32_t code)
>>  {
>>      SCLPDevice *sclp = get_sclp_device();
>> diff --git a/include/hw/s390x/sclp.h b/include/hw/s390x/sclp.h
>> index c54413b78c..c0a3faa37d 100644
>> --- a/include/hw/s390x/sclp.h
>> +++ b/include/hw/s390x/sclp.h
>> @@ -217,5 +217,7 @@ void s390_sclp_init(void);
>>  void sclp_service_interrupt(uint32_t sccb);
>>  void raise_irq_cpu_hotplug(void);
>>  int sclp_service_call(CPUS390XState *env, uint64_t sccb, uint32_t code);
>> +int sclp_service_call_protected(CPUS390XState *env, uint64_t sccb,
>> +                                uint32_t code);
>>  
>>  #endif
>> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
>> index 3d9c44ba9d..b802d02ff5 100644
>> --- a/target/s390x/kvm.c
>> +++ b/target/s390x/kvm.c
>> @@ -1174,6 +1174,11 @@ static void kvm_sclp_service_call(S390CPU *cpu, struct kvm_run *run,
>>      sccb = env->regs[ipbh0 & 0xf];
>>      code = env->regs[(ipbh0 & 0xf0) >> 4];
>>  
>> +    if (run->s390_sieic.icptcode == ICPT_PV_INSTR) {
> 
> isn't checking against env->pv easier and cleaner?

Hmm, I dislike checking a global state for a CPU icpt.

> 
> 



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