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

[David Hildenbrand]

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 ....

Can we move that into s390_get_feat_block instead and check against the
feature bit instead?

-- 
Thanks,

David / dhildenb