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Tue, 20 May 2025 14:34:29 +0000 (GMT) Message-ID: <0b90cd0ad24727c9d7b110f09fd79b2525b4fbe1.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: Tue, 20 May 2025 16:34:30 +0200 In-Reply-To: <8373c4a476e6a8f714a559d0fad8f3fed66089f1.camel@linux.ibm.com> References: <20250514163855.124471-1-imbrenda@linux.ibm.com> <20250514163855.124471-3-imbrenda@linux.ibm.com> <8373c4a476e6a8f714a559d0fad8f3fed66089f1.camel@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-Authority-Analysis: v=2.4 cv=J/mq7BnS c=1 sm=1 tr=0 ts=682c92fb cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=dt9VzEwgFbYA:10 a=VnNF1IyMAAAA:8 a=mH3vZ3oXfMAmPE_1c18A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNTIwMDExMyBTYWx0ZWRfX4M43be9fidUy OuGsDr1NmuGi8aSY0WamN+xb1/b9dBe2hzJ5PyptZf/oku0/T0enf8QlfkhJpupi8hw/GpwnRvo u059uov+VAnVCyOrHlerONKahbnfxVnfH9Krvz0QWGTwUtgHiAMv3gY/aHf2ObQ7+bPrLzHDFuJ xJB4qA6RMCdyUGHgJtH6hJ5kki65A27Laik8LYQvQyLYtW4Gsir4D7jJUvGldVAbDkt/4Bs1/8d ecr8/EnEaCxMWOTx/w4DnaoSCJu4SpAk3MNx1p3TRA+RgwQQFJzoBJF4v0y3rUWP5ay7ARLSNnx lzV2OJyhsZ/QPULzYwODdMPRR/PODbaoKu2KInM1gHY3aHGkQFD5uPL9qwkLN9dokqWFnF8je55 WFtsv6yZhuZY2OD3WUZ7MU82oO1S+25UgL1lDjh3Q/vBcvLibHEfxLDBdB8nYTvZJVbiufeW X-Proofpoint-ORIG-GUID: qpZcX6c6IVm_wymNTKzRyJj5b9rijhVt X-Proofpoint-GUID: qpZcX6c6IVm_wymNTKzRyJj5b9rijhVt 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=2025-05-20_06,2025-05-16_03,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 priorityscore=1501 impostorscore=0 bulkscore=0 mlxlogscore=929 mlxscore=0 clxscore=1015 phishscore=0 spamscore=0 lowpriorityscore=0 malwarescore=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-2505200113 On Mon, 2025-05-19 at 16:42 +0200, Nina Schoetterl-Glausch wrote: > 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 >=20 > Reviewed-by: Nina Schoetterl-Glausch >=20 > 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 nee= ds > to be held. I think this would be good to have if you really don't want t= he > srcu_read_lock here. > But then you might also want that documented up the call chain. Actually, can we use __must_hold or have some assert? >=20 > > --- > > 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