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Thu, 16 Apr 2026 07:00:58 +0000 (GMT) Date: Thu, 16 Apr 2026 09:00:57 +0200 From: Alexander Gordeev To: Heiko Carstens Cc: Kevin Brodsky , David Hildenbrand , Andrew Morton , Gerald Schaefer , Christian Borntraeger , Vasily Gorbik , Claudio Imbrenda , linux-s390@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 6/6] s390/mm: Allow lazy MMU mode disabling Message-ID: <2a497bff-1773-4245-a63c-784ed8853b11-agordeev@linux.ibm.com> References: <24d843c5568a8b591cbbe16eca092e7f45d18cf5.1776264097.git.agordeev@linux.ibm.com> <20260416054405.10407B6c-hca@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260416054405.10407B6c-hca@linux.ibm.com> X-TM-AS-GCONF: 00 X-Proofpoint-GUID: i30Fjl33Inahe3fkQUhSbi2uCpwkt34E X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDE2MDA2MiBTYWx0ZWRfX/2vOhPPcKvXc WK6/l1A12P8h3ZP2yfx/j2LMudfxp0UCndGSoqXkxgtmZHnVs9cxUp78MM6DaB0xH83+JzQO/Fe WHmONGSbdOQ3fMjSvuZ/V44KzMe5xDDi3D3smgAEH5BeVD1GIJluOzjKlNK5aP5DWmi3zoE+/aH I4LSO4RHkWbVBYLwHZjBRZwgzHByL2vC4SRKbnP2NvKICgycje8DNJS9Evt7l0fGY2YmWuG7vUG SClN+gejL3roR3e12Q1AcEETd9lmTkmoEaUmSPEx4zz9/wa4c4BHtohF4o33tdLrBNNErIKuUfS F+knZw7WiHWvCr+9n8wU/kTHuEzvpbzaAiDMdmB0Jqyl1Mv4RbV+DWZ4/d+t3TGvP2wFpK97+Ou 48XidNPdeJC1SJUx/8EXyR3WU4kFLyMP6U9r+P8UjciQRR/nkQqgqipRCNwHtU4u20Fx6GHgQ7q 9Kw++wK02bkPuc1q2fQ== X-Proofpoint-ORIG-GUID: i30Fjl33Inahe3fkQUhSbi2uCpwkt34E X-Authority-Analysis: v=2.4 cv=W60IkxWk c=1 sm=1 tr=0 ts=69e08930 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=kj9zAlcOel0A:10 a=A5OVakUREuEA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=ov5kqanpoNFzf825lJoA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-04-16_02,2026-04-13_04,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 clxscore=1015 priorityscore=1501 spamscore=0 bulkscore=0 adultscore=0 phishscore=0 lowpriorityscore=0 suspectscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604070000 definitions=main-2604160062 On Thu, Apr 16, 2026 at 07:44:05AM +0200, Heiko Carstens wrote: > > @@ -169,6 +185,8 @@ void arch_enter_lazy_mmu_mode_for_pte_range(struct mm_struct *mm, > > { > > if (!test_facility(13)) > > return; > > + if (!static_branch_likely(&lazy_mmu)) > > + return; > > Looks like there is an alternative chicken switch available: remove > facility bit 13 from the facility list via kernel command line option. > > Unless I am mistaken: that should be sufficient and avoids adding more > code. But that would also withdraw multi-IPTE from other unrelated parts of the code, e.g. from __kernel_map_pages().