Re: [PATCH v8 2/2] s390/kvm: diagnose 0x318 sync and reset

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 22.06.20 12:24, Cornelia Huck wrote:
> On Thu, 18 Jun 2020 18:22:22 -0400
> Collin Walling <walling@linux.ibm.com> wrote:
> 
>> DIAGNOSE 0x318 (diag318) sets information regarding the environment
>> the VM is running in (Linux, z/VM, etc) and is observed via
>> firmware/service events.
>>
>> This is a privileged s390x instruction that must be intercepted by
>> SIE. Userspace handles the instruction as well as migration. Data
>> is communicated via VCPU register synchronization.
>>
>> The Control Program Name Code (CPNC) is stored in the SIE block. The
>> CPNC along with the Control Program Version Code (CPVC) are stored
>> in the kvm_vcpu_arch struct.
>>
>> The CPNC is shadowed/unshadowed in VSIE.
>>
>> This data is reset on load normal and clear resets.
>>
>> Signed-off-by: Collin Walling <walling@linux.ibm.com>
>> ---
>>  arch/s390/include/asm/kvm_host.h |  4 +++-
>>  arch/s390/include/uapi/asm/kvm.h |  5 ++++-
>>  arch/s390/kvm/kvm-s390.c         | 11 ++++++++++-
>>  arch/s390/kvm/vsie.c             |  3 +++
>>  include/uapi/linux/kvm.h         |  1 +
>>  5 files changed, 21 insertions(+), 3 deletions(-)
>>
> 
> (...)
> 
>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>> index 4fdf30316582..35cdb4307904 100644
>> --- a/include/uapi/linux/kvm.h
>> +++ b/include/uapi/linux/kvm.h
>> @@ -1031,6 +1031,7 @@ struct kvm_ppc_resize_hpt {
>>  #define KVM_CAP_PPC_SECURE_GUEST 181
>>  #define KVM_CAP_HALT_POLL 182
>>  #define KVM_CAP_ASYNC_PF_INT 183
>> +#define KVM_CAP_S390_DIAG318 184
> 
> Do we strictly need this new cap, or would checking against the sync
> regs capabilities be enough?

We could check the sync_regs valid field to decide about the sync. We do
that for ETOKEN as well and QEMU also uses it in handle_diag_318.

I think what this is used for is actually to tell the QEMU CPU model
if this is there. And for that the sync_reg validity seems wrong. So better
keep the CAP?