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References: <20221117221758.66326-1-scgl@linux.ibm.com> <20221117221758.66326-3-scgl@linux.ibm.com> <f96b50e2-24ac-4016-d3f1-ffc375516e7c@redhat.com> <e735fa2cde6e9c92dda134634cb3d67b64b23fe9.camel@linux.ibm.com>
Subject: Re: [PATCH v3 2/9] Documentation: KVM: s390: Describe KVM_S390_MEMOP_F_CMPXCHG
To:     Alexander Gordeev <agordeev@linux.ibm.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Janis Schoetterl-Glausch <scgl@linux.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        Thomas Huth <thuth@redhat.com>,
        Vasily Gorbik <gor@linux.ibm.com>
Cc:     David Hildenbrand <david@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>, kvm@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-kselftest@vger.kernel.org, linux-s390@vger.kernel.org,
        Paolo Bonzini <pbonzini@redhat.com>,
        Shuah Khan <shuah@kernel.org>,
        Sven Schnelle <svens@linux.ibm.com>
From:   Nico Boehr <nrb@linux.ibm.com>
Message-ID: <166936633695.19077.13372353298394327779@t14-nrb.local>
User-Agent: alot/0.8.1
Date:   Fri, 25 Nov 2022 09:52:18 +0100
Precedence: bulk

Quoting Janis Schoetterl-Glausch (2022-11-22 14:10:41)
> On Tue, 2022-11-22 at 08:47 +0100, Thomas Huth wrote:
> > On 17/11/2022 23.17, Janis Schoetterl-Glausch wrote:
[...]
> > >   Supported flags:
> > >     * ``KVM_S390_MEMOP_F_CHECK_ONLY``
> > >     * ``KVM_S390_MEMOP_F_SKEY_PROTECTION``
> > > +  * ``KVM_S390_MEMOP_F_CMPXCHG``
> > > +
> > > +The semantics of the flags common with logical acesses are as for lo=
gical
> > > +accesses.
> > > +
> > > +For write accesses, the KVM_S390_MEMOP_F_CMPXCHG might be supported.
> >=20
> > I'd maybe merge this with the last sentence:
> >=20
> > For write accesses, the KVM_S390_MEMOP_F_CMPXCHG flag is supported if=20
> > KVM_CAP_S390_MEM_OP_EXTENSION has bit 1 (i.e. bit with value 2) set.
>=20
> Ok.
> >=20
> > ... and speaking of that, I wonder whether it's maybe a good idea to=20
> > introduce some #defines for bit 1 / value 2, to avoid the confusion ?
>=20
> Not sure, I don't feel it's too complicated. Where would you define it?
> Next to the mem_op struct? KVM_S390_MEMOP_EXTENSION_CAP_CMPXCHG?

I think the define would be a good idea. Location and name sound good to me.

You could also replace the hard-coded 0x3 in kvm_vm_ioctl_check_extension()=
 when you have the define.