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Mon, 21 Nov 2022 17:44:42 +0000 (GMT) Received: from li-7e0de7cc-2d9d-11b2-a85c-de26c016e5ad.ibm.com (unknown [9.171.52.183]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 21 Nov 2022 17:44:42 +0000 (GMT) Message-ID: Subject: Re: [PATCH v3 2/9] Documentation: KVM: s390: Describe KVM_S390_MEMOP_F_CMPXCHG From: Janis Schoetterl-Glausch To: Bagas Sanjaya , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Heiko Carstens , Vasily Gorbik , Alexander Gordeev Cc: David Hildenbrand , Jonathan Corbet , 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 , Shuah Khan , Sven Schnelle Date: Mon, 21 Nov 2022 18:44:42 +0100 In-Reply-To: <73ecf737-c523-b4ab-f11f-431bb5fb2c37@gmail.com> References: <20221117221758.66326-1-scgl@linux.ibm.com> <20221117221758.66326-3-scgl@linux.ibm.com> <73ecf737-c523-b4ab-f11f-431bb5fb2c37@gmail.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.42.4 (3.42.4-2.fc35) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: xcZfCWc2vgaEHtwQ26s-Mj0whSdSWr9i X-Proofpoint-ORIG-GUID: olU0MKShioiM4yJlr6NsYzJVdYNWNhc0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.219,Aquarius:18.0.895,Hydra:6.0.545,FMLib:17.11.122.1 definitions=2022-11-21_14,2022-11-18_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 bulkscore=0 phishscore=0 malwarescore=0 impostorscore=0 mlxscore=0 clxscore=1015 priorityscore=1501 suspectscore=0 spamscore=0 mlxlogscore=765 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2210170000 definitions=main-2211210132 Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org 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.