From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx0b-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6016E332604; Thu, 16 Apr 2026 08:22:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.163.158.5 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776327745; cv=none; b=pZfumisZhLNdUlKUsfGoDoaOvF/rsVI/bIAQK2HX8QpEt3ypc2ySxhaOWeMD+qmaNQaB76uX3kMNCNbW4UZa0uRWtsGvxjssI8z+x9QbYZQeP3bIr9JbMC67H96oYDe9ET/achHOjxAwr2YtLUvgM/s4nmms59zwaHLXcbEv31g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776327745; c=relaxed/simple; bh=+annyCviDXRU6aLD48jWyvslETh/Cvy2LZ5NRoqrRpA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=XIIjS9hzU4TeItu7QBGpeSHCms2txNLyOGIywmBEIrqrcRJWSR7ZUWmhmdHtEp21outPhS/tUm9tXwfuL69DOcKOWBTJr9LOKYjbWqEAdbXeSSUXIUxozogXjuDtSdfgAr3pLGH3ZUJaj8/f+jQ9OQ9dg1SrwAS2HE4JCCV0zFc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com; spf=pass smtp.mailfrom=linux.ibm.com; dkim=pass (2048-bit key) header.d=ibm.com header.i=@ibm.com header.b=e2Fj1hLf; arc=none smtp.client-ip=148.163.158.5 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=ibm.com header.i=@ibm.com header.b="e2Fj1hLf" Received: from pps.filterd (m0353725.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 63G6Edg91733184; Thu, 16 Apr 2026 08:22:16 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=cc :content-transfer-encoding:content-type:date:from:in-reply-to :message-id:mime-version:references:subject:to; s=pp1; bh=EghXYY nkmIraQBRylz8V08Xw1Fw8PiFljL3GV4sjMm0=; b=e2Fj1hLfI0Z8Po/oWJGVW0 kG/Su8H3VxOIUcJipozN8A1Nh5d8pn6dKbMb4XGpU8+r3sqys4Un10OW+VGpyloE T2L4eq1Kj+ZxvDazOTJXRV1PAjI6D1DvWAMlJTWzE/YnUEzYghxhOZeuGBSmFC8w wdS5PjkoG4zUb3IjvVyBBNJWh5J3lni9lg9QlQdNKSMDNpZxJg5tz4Nt40UT8CHr R/cG8ESBb9p6eVhIk9AfoVlZApcVSUhmDd8dfkvJwMHqgGophpEU3sy6RxfCSw2C fumrNuHk+2nH2AmQ/www7b6lqruiOK1ZBfqZwJN3O/+JhJ4p0dVYx+sJ4n5f3xxw == Received: from ppma12.dal12v.mail.ibm.com (dc.9e.1632.ip4.static.sl-reverse.com [50.22.158.220]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 4dh89mbk9e-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 16 Apr 2026 08:22:16 +0000 (GMT) Received: from pps.filterd (ppma12.dal12v.mail.ibm.com [127.0.0.1]) by ppma12.dal12v.mail.ibm.com (8.18.1.2/8.18.1.2) with ESMTP id 63G6FXdP015164; Thu, 16 Apr 2026 08:22:15 GMT Received: from smtprelay06.fra02v.mail.ibm.com ([9.218.2.230]) by ppma12.dal12v.mail.ibm.com (PPS) with ESMTPS id 4dg0mst7rd-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 16 Apr 2026 08:22:15 +0000 Received: from smtpav06.fra02v.mail.ibm.com (smtpav06.fra02v.mail.ibm.com [10.20.54.105]) by smtprelay06.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 63G8MCti27984192 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 16 Apr 2026 08:22:12 GMT Received: from smtpav06.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 243C02004D; Thu, 16 Apr 2026 08:22:12 +0000 (GMT) Received: from smtpav06.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B4A1C20049; Thu, 16 Apr 2026 08:22:11 +0000 (GMT) Received: from [9.52.200.39] (unknown [9.52.200.39]) by smtpav06.fra02v.mail.ibm.com (Postfix) with ESMTP; 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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.