Re: [PATCH v3 2/9] Documentation: KVM: s390: Describe KVM_S390_MEMOP_F_CMPXCHG

Janis Schoetterl-Glausch
2022-11-21T17:45:00Z

On Fri, 2022-11-18 at 08:50 +0700, Bagas Sanjaya wrote:
> On 11/18/22 05:17, Janis Schoetterl-Glausch wrote:
> > +For write accesses, the KVM_S390_MEMOP_F_CMPXCHG might be supported.
> > +In this case, instead of doing an unconditional write, the access occurs only
> > +if the target location contains the "size" byte long value pointed to by
> > +"old_p". This is performed as an atomic cmpxchg. "size" must be a power of two
> > +up to and including 16.
> > +The value at the target location is written to the location "old_p" points to.
> > +If the exchange did not take place because the target value doesn't match the
> > +old value KVM_S390_MEMOP_R_NO_XCHG is returned.
> > +The KVM_S390_MEMOP_F_CMPXCHG flag is supported if KVM_CAP_S390_MEM_OP_EXTENSION
> > +has bit 1 (i.e. bit with value 2) set.
> >
>
> Is KVM_S390_MEMOP_F_CMPXCHG supported with conditions (as you implied)?
>
I'm afraid I don't quite understand the question.
It is supported if the capability says it is, i.e. if bit 1 is set.