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Mon, 25 Nov 2024 11:50:43 +0000 Received: from smtpav03.fra02v.mail.ibm.com (smtpav03.fra02v.mail.ibm.com [10.20.54.102]) by smtprelay05.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 4APBoeTV56557988 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 25 Nov 2024 11:50:40 GMT Received: from smtpav03.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 0D3742004D; Mon, 25 Nov 2024 11:50:40 +0000 (GMT) Received: from smtpav03.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id DF49C2004B; Mon, 25 Nov 2024 11:50:39 +0000 (GMT) Received: from tuxmaker.lnxne.boe (unknown [9.152.85.9]) by smtpav03.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 25 Nov 2024 11:50:39 +0000 (GMT) From: Heiko Carstens To: Christian Borntraeger , Janosch Frank , Claudio Imbrenda , David Hildenbrand Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 2/3] KVM: s390: Remove one byte cmpxchg() usage Date: Mon, 25 Nov 2024 12:50:38 +0100 Message-ID: <20241125115039.1809353-3-hca@linux.ibm.com> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20241125115039.1809353-1-hca@linux.ibm.com> References: <20241125115039.1809353-1-hca@linux.ibm.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: a6K4xVPleESxgCAbo4yBKA50sVjBgnag X-Proofpoint-GUID: a6K4xVPleESxgCAbo4yBKA50sVjBgnag X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1051,Hydra:6.0.680,FMLib:17.12.62.30 definitions=2024-10-15_01,2024-10-11_01,2024-09-30_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 malwarescore=0 mlxlogscore=944 spamscore=0 suspectscore=0 phishscore=0 clxscore=1015 mlxscore=0 lowpriorityscore=0 impostorscore=0 adultscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2409260000 definitions=main-2411250094 Within sca_clear_ext_call() cmpxchg() is used to clear one or two bytes (depending on sca format). The cmpxchg() calls are not supposed to fail; if so that would be a bug. Given that cmpxchg() usage on one and two byte areas generates very inefficient code, replace them with block concurrent WRITE_ONCE() calls, and remove the WARN_ON(). Signed-off-by: Heiko Carstens Acked-by: Claudio Imbrenda --- arch/s390/kvm/interrupt.c | 13 ++----------- 1 file changed, 2 insertions(+), 11 deletions(-) diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c index eff69018cbeb..3fd21037479f 100644 --- a/arch/s390/kvm/interrupt.c +++ b/arch/s390/kvm/interrupt.c @@ -118,8 +118,6 @@ static int sca_inject_ext_call(struct kvm_vcpu *vcpu, int src_id) static void sca_clear_ext_call(struct kvm_vcpu *vcpu) { - int rc, expect; - if (!kvm_s390_use_sca_entries()) return; kvm_s390_clear_cpuflags(vcpu, CPUSTAT_ECALL_PEND); @@ -128,23 +126,16 @@ static void sca_clear_ext_call(struct kvm_vcpu *vcpu) struct esca_block *sca = vcpu->kvm->arch.sca; union esca_sigp_ctrl *sigp_ctrl = &(sca->cpu[vcpu->vcpu_id].sigp_ctrl); - union esca_sigp_ctrl old; - old = READ_ONCE(*sigp_ctrl); - expect = old.value; - rc = cmpxchg(&sigp_ctrl->value, old.value, 0); + WRITE_ONCE(sigp_ctrl->value, 9); } else { struct bsca_block *sca = vcpu->kvm->arch.sca; union bsca_sigp_ctrl *sigp_ctrl = &(sca->cpu[vcpu->vcpu_id].sigp_ctrl); - union bsca_sigp_ctrl old; - old = READ_ONCE(*sigp_ctrl); - expect = old.value; - rc = cmpxchg(&sigp_ctrl->value, old.value, 0); + WRITE_ONCE(sigp_ctrl->value, 0); } read_unlock(&vcpu->kvm->arch.sca_lock); - WARN_ON(rc != expect); /* cannot clear? */ } int psw_extint_disabled(struct kvm_vcpu *vcpu)