Re: [PATCH 2/2] s390x: pv: Fix diag318 PV fencing

[Christian Borntraeger]

On 21.10.20 16:14, David Hildenbrand wrote:
> On 21.10.20 15:43, Janosch Frank wrote:
>> Diag318 fencing needs to be determined on the current VM PV state and
>> not on the state that the VM has when we create the CPU model.
>>
>> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
>> Reported-by: Marc Hartmayer <mhartmay@linux.ibm.com>
>> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
>> Fixes: fabdada935 ("s390: guest support for diagnose 0x318")
>> Tested-by: Marc Hartmayer <mhartmay@linux.ibm.com>
>> ---
>>  hw/s390x/sclp.c    | 10 ++++++++++
>>  target/s390x/kvm.c |  3 +--
>>  2 files changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
>> index 0cf2290826..69aba402d3 100644
>> --- a/hw/s390x/sclp.c
>> +++ b/hw/s390x/sclp.c
>> @@ -22,6 +22,7 @@
>>  #include "hw/s390x/event-facility.h"
>>  #include "hw/s390x/s390-pci-bus.h"
>>  #include "hw/s390x/ipl.h"
>> +#include "hw/s390x/pv.h"
>>  
>>  static inline SCLPDevice *get_sclp_device(void)
>>  {
>> @@ -142,6 +143,15 @@ static void read_SCP_info(SCLPDevice *sclp, SCCB *sccb)
>>      if (s390_has_feat(S390_FEAT_EXTENDED_LENGTH_SCCB)) {
>>          s390_get_feat_block(S390_FEAT_TYPE_SCLP_FAC134,
>>                              &read_info->fac134);
>> +        /*
>> +         * Diag318 is not available in protected mode and will result
>> +         * in an operation exception. As we can dynamically move in
>> +         * and out of protected mode, we need to fence the feature
>> +         * here rather than when creating the CPU model.
>> +         */
>> +        if (s390_is_pv()) {
>> +            read_info->fac134 &= ~0x80;
>> +        }
> 
> Hmm, I thought firmware would handle exposing cpu features and similar,
> so we can't temper with it ....

Only the stfle bits. 
> 
> Can we move that into s390_get_feat_block instead and check against the
> feature bit instead?

No because we want to have this active for !pv and disabled for pv but we switch
this multiple times when doing boot/reboot.