linux-kernel - Re: [PATCH v3 2/9] Documentation: KVM: s390: Describe KVM_S390_MEMOP_F

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Message-ID: <e56e2c58477626dbdc6d4ddcd806459e7ce93b28.camel@linux.ibm.com>
Date:   Mon, 21 Nov 2022 18:44:42 +0100
From:   Janis Schoetterl-Glausch <scgl@...ux.ibm.com>
To:     Bagas Sanjaya <bagasdotme@...il.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Jonathan Corbet <corbet@....net>, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-s390@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Shuah Khan <shuah@...nel.org>,
        Sven Schnelle <svens@...ux.ibm.com>
Subject: Re: [PATCH v3 2/9] Documentation: KVM: s390: Describe
 KVM_S390_MEMOP_F_CMPXCHG

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.