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Thu, 16 Apr 2026 08:22:11 +0000 (GMT) Message-ID: <161ab40c-dad7-42b4-b6ad-917f8249254a@linux.ibm.com> Date: Thu, 16 Apr 2026 10:22:11 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 6/6] s390/mm: Allow lazy MMU mode disabling To: Alexander Gordeev , Heiko Carstens Cc: Kevin Brodsky , David Hildenbrand , Andrew Morton , Gerald Schaefer , Vasily Gorbik , Claudio Imbrenda , linux-s390@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <24d843c5568a8b591cbbe16eca092e7f45d18cf5.1776264097.git.agordeev@linux.ibm.com> <20260416054405.10407B6c-hca@linux.ibm.com> <2a497bff-1773-4245-a63c-784ed8853b11-agordeev@linux.ibm.com> Content-Language: en-US From: Christian Borntraeger In-Reply-To: <2a497bff-1773-4245-a63c-784ed8853b11-agordeev@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=I/dVgtgg c=1 sm=1 tr=0 ts=69e09c38 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=A5OVakUREuEA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=bZTvA-38IwGshgt2pOQA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: cybN27AT70Xlug33CcVsFDGHqa-ZO9sJ X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDE2MDA3NyBTYWx0ZWRfX2Uocvty7Sfzg 3EKlGo+vHAXe/bxw3gU+c95Q5guzP+mOtWdsoQvd1m49GlwN8B4zgT/2IRWbjrCf8Z8Ez6/mhfC cl+WXtWMpsbbF+rCwcVMWO1nRPPLVuOPAYWHPJ/gyZHbY53pRHZGfysgBskJH6/sHsPvq614gNR NK9IvglftKx10tyLUhewEHJ2IyvDcizzTPZ2eKIZzvF2eB+ivmeMoJoJHYdxaAYslB4Py3SUvV6 +synpXrscZek6LfanKvVHcCuwdMzjruRvxdXfhqpz95+kEqqzS4HLihEXPYoyOT7+kJEmsk6byM dgym7Y0ddR1mmu7cLNdAcUFbaNbtzOnlIJdWWashK4VP/5eNnkMcKTkmA20aOEw0iTsqe3sNm6j JOruNSZ63uJCCxs1b+UGCrP+cMo+7+FkZbFZIhLT4CfyuHBXV6aAKfY0Y0m6fQPZapYTIhQh+FP qmEiz7gMaXcyn+nZqhQ== X-Proofpoint-ORIG-GUID: cybN27AT70Xlug33CcVsFDGHqa-ZO9sJ 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 malwarescore=0 bulkscore=0 clxscore=1011 adultscore=0 lowpriorityscore=0 suspectscore=0 impostorscore=0 phishscore=0 spamscore=0 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604070000 definitions=main-2604160077 X-Stat-Signature: 8he48yikh3bw3czeznaxura9s7on7agu X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: E436BC000B X-HE-Tag: 1776327739-786017 X-HE-Meta: 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 kdvIRwOP msxr8TCNW5Lef8MYKj0c/beVe23t0accA8TCc83RD6pRQQWjH5XHlgiENKRBZPFaYha2NJ8v9qTEcIdBVXEUPV+C0msEL35/rxIfzV529SlkyePmhm2OrsP+YfrnuzD0mewkrnjIEvKBt6ZDXHbo3b9KzRF/CrjgldhFsYJsmxF7EPznwv+uGFsnZ24dJGGqmi6fYJj/5fP+zp/fx3vphs4mK/fgWLlrfwqq3FD2zM46SLV+HF7Mir2KfeWPBysG0BQrtoohN60frEmbQkXxL9/8Janj+jqcIb5/011B56yxG/EPfNyfR62l2JuT7O3Vz4QKn Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Am 16.04.26 um 09:00 schrieb Alexander Gordeev: > 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(). Which is fine. Do not over-optimize for a case that should not be needed unless we really mess up. This parameter is way too complicated to ever be set/unset by a customer.