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Thu, 2 Jul 2026 17:08:06 +0000 (GMT) Received: from li-479af74c-31f9-11b2-a85c-e4ddee11713b.ibm.com (unknown [9.61.136.69]) by smtpav06.dal12v.mail.ibm.com (Postfix) with ESMTP; Thu, 2 Jul 2026 17:08:06 +0000 (GMT) Message-ID: <6f251f37b0aa2b829769d59bb3e4f6d494484750.camel@linux.ibm.com> Subject: Re: [PATCH v1 3/8] KVM: s390: Fix unlikely race with KVM_CAP_S390_USER_OPEREXEC From: Eric Farman To: Claudio Imbrenda , linux-kernel@vger.kernel.org Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org, borntraeger@de.ibm.com, frankja@linux.ibm.com, david@kernel.org, seiden@linux.ibm.com, nrb@linux.ibm.com, schlameuss@linux.ibm.com, gra@linux.ibm.com Date: Thu, 02 Jul 2026 13:08:06 -0400 In-Reply-To: <20260702152406.204782-4-imbrenda@linux.ibm.com> References: <20260702152406.204782-1-imbrenda@linux.ibm.com> <20260702152406.204782-4-imbrenda@linux.ibm.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.58.3 (3.58.3-1.fc43) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: Bu1nPldO9y19wGYeoTPqQ2JmXwS4OTnK X-Proofpoint-Spam-Info: AW1haW4tMjYwNzAyMDE3NyBTYWx0ZWRfXz8SQtCO2eUrP mDJVjA2wU5zX7U7LXYpjKMqCDWhXyEOYxJjrviiycDXtGGwKIeVUlfjf2Wj4gkvtdCSpfUvkYmI 905TOHsnLaKGX6aYy/U8NoNjFPBG6BM= X-Authority-Analysis: v=2.4 cv=edsNubEH c=1 sm=1 tr=0 ts=6a469af9 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VnNF1IyMAAAA:8 a=UTdIPT0w00pXnvBMiBYA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzAyMDE3NyBTYWx0ZWRfX87HSXYfA2OQg d9V4cQ3YY0Dvg4W+k3vTPuvZzLYZGRypKDrAlQB9bUlDxkJngMK8IsJai+ZofKveDCvZYdWFkpG CvNIuydrSW335F6XiHTmJYotp7eFhAxekREosQD06jMvqmZlkgkA2fYBEi4fqtg860Zoj8bqU0l CFie7lwAyYJnvv0f1EUmXH8AcNh9ucxfBbny8vW9KWxh1xo+bjIxfY3LWmhHpwq5K+gWIIgbheo x9z5oiF/XCqbfeVCwqdocw18euwWxQtPRBMWZaTyXSZqUfBNRj9OJEeJKJaEczqLvFWOWISLJg9 rKIgJRbG5pnRONf9O9KyR2X3wQGSlovCYOSutbNWQjjR1wXo2qMOlCUa/R3IoJ3VZwPGPhCg0gA H9G16eZE3LWT6W5ZbNLr65VzmvnkFM/9SZGW5JOT3SYiQnpFuVHBLIO0dlv5y07ZWAtVfT3VChb 721T7mqnR3DKLT85QwA== X-Proofpoint-ORIG-GUID: Bu1nPldO9y19wGYeoTPqQ2JmXwS4OTnK X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-07-02_02,2026-06-26_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 adultscore=0 impostorscore=0 bulkscore=0 spamscore=0 suspectscore=0 clxscore=1011 lowpriorityscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607020177 On Thu, 2026-07-02 at 17:24 +0200, Claudio Imbrenda wrote: > Due to a missing barrier, it was theoretically possible that a vCPU > being created concurrently with enabling KVM_CAP_S390_USER_OPEREXEC > would end up with the capability not enabled. >=20 > Fix by using WRITE_ONCE(), which is enough on s390. >=20 > Fixes: 8e8678e740ec ("KVM: s390: Add capability that forwards operation e= xceptions") > Signed-off-by: Claudio Imbrenda > --- > arch/s390/kvm/kvm-s390.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Thanks, Claudio. FWIW, Reviewed-by: Eric Farman >=20 > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c > index 4a6d903e3523..784f7d9c79c7 100644 > --- a/arch/s390/kvm/kvm-s390.c > +++ b/arch/s390/kvm/kvm-s390.c > @@ -955,7 +955,7 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct k= vm_enable_cap *cap) > break; > case KVM_CAP_S390_USER_OPEREXEC: > VM_EVENT(kvm, 3, "%s", "ENABLE: CAP_S390_USER_OPEREXEC"); > - kvm->arch.user_operexec =3D 1; > + WRITE_ONCE(kvm->arch.user_operexec, 1); > icpt_operexc_on_all_vcpus(kvm); > r =3D 0; > break;