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Mon, 19 May 2025 14:42:55 +0000 (GMT) Message-ID: <8373c4a476e6a8f714a559d0fad8f3fed66089f1.camel@linux.ibm.com> Subject: Re: [PATCH v1 2/5] KVM: s390: remove unneeded srcu lock From: Nina Schoetterl-Glausch To: Claudio Imbrenda , linux-kernel@vger.kernel.org Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org, frankja@linux.ibm.com, borntraeger@de.ibm.com, seiden@linux.ibm.com, nrb@linux.ibm.com, david@redhat.com, hca@linux.ibm.com, agordeev@linux.ibm.com, svens@linux.ibm.com, gor@linux.ibm.com Date: Mon, 19 May 2025 16:42:55 +0200 In-Reply-To: <20250514163855.124471-3-imbrenda@linux.ibm.com> References: <20250514163855.124471-1-imbrenda@linux.ibm.com> <20250514163855.124471-3-imbrenda@linux.ibm.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.1 (3.56.1-1.fc42) Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNTE5MDEzNSBTYWx0ZWRfX9JB+3b8XV/QD +v4QIoyM4LQ0YKQO2skMiElEpiAlKKu8FuqvK75YciQpRn0xhEwdJAhMS5F8v6He9JRtcsEG263 bihdZACvndctZjF5jy/NdPaYgQ/J/61KyLvzn2PFSwkVCJsgCy7QyzGDjWjMFH3lWzCKAfoOM1X 29ga4jKqK0n18asg8aKt2z4SmYQbEEiVUIdV2ZesTYXhdlRZ7VcP6cxkEgXP/e7rpA+ODYRFDiK cAGW3zTOITZJANxdkpxzmW5EEidUvL1JsafWdbu/zcyUu5j2gn3PzTLIBblKZ8ofC1Fbx3RD8DD 95h9OEx8W4Vy9XxsTHJqMIsLZ8Yjk48c/a+cuKCa023P/smbJqhLQAjOHWxK7nhWpvH388F0ohv JLeWDq+duWGrY5leXaYSniLLXupGcY1N5+zEvMBIkduRF/qWnzeYWHVKNDKXaYtvJE3T3Wpj X-Proofpoint-ORIG-GUID: Kvm0tqNSrvW0som2LyxP5btC7jvBweJ5 X-Proofpoint-GUID: Kvm0tqNSrvW0som2LyxP5btC7jvBweJ5 X-Authority-Analysis: v=2.4 cv=P406hjAu c=1 sm=1 tr=0 ts=682b4374 cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=IkcTkHD0fZMA:10 a=dt9VzEwgFbYA:10 a=VnNF1IyMAAAA:8 a=8L8LAccZYskMU-B2xLIA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.0.736,FMLib:17.12.80.40 definitions=2025-05-19_06,2025-05-16_03,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 clxscore=1011 mlxscore=0 adultscore=0 impostorscore=0 spamscore=0 malwarescore=0 priorityscore=1501 mlxlogscore=999 bulkscore=0 phishscore=0 suspectscore=0 classifier=spam authscore=0 authtc=n/a authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2505070000 definitions=main-2505190135 On Wed, 2025-05-14 at 18:38 +0200, Claudio Imbrenda wrote: > All paths leading to handle_essa() already hold the kvm->srcu. > Remove unneeded srcu locking from handle_essa(). >=20 > Signed-off-by: Claudio Imbrenda Reviewed-by: Nina Schoetterl-Glausch Why are you removing it tho? It should be very low cost and it makes the code more robust, since handle_essa itself ensures that it has the lock. It is also easier to understand which synchronization the function does. You could of course add a comment stating that the kvm srcu read side needs to be held. I think this would be good to have if you really don't want the srcu_read_lock here. But then you might also want that documented up the call chain. > --- > arch/s390/kvm/priv.c | 4 ---- > 1 file changed, 4 deletions(-) >=20 > diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c > index 1a49b89706f8..758cefb5bac7 100644 > --- a/arch/s390/kvm/priv.c > +++ b/arch/s390/kvm/priv.c > @@ -1297,12 +1297,8 @@ static int handle_essa(struct kvm_vcpu *vcpu) > /* Retry the ESSA instruction */ > kvm_s390_retry_instr(vcpu); > } else { > - int srcu_idx; > - > mmap_read_lock(vcpu->kvm->mm); > - srcu_idx =3D srcu_read_lock(&vcpu->kvm->srcu); > i =3D __do_essa(vcpu, orc); > - srcu_read_unlock(&vcpu->kvm->srcu, srcu_idx); > mmap_read_unlock(vcpu->kvm->mm); > if (i < 0) > return i; --=20 IBM Deutschland Research & Development GmbH Vorsitzender des Aufsichtsrats: Wolfgang Wendt Gesch=C3=A4ftsf=C3=BChrung: David Faller Sitz der Gesellschaft: B=C3=B6blingen / Registergericht: Amtsgericht Stuttg= art, HRB 243294