From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6D5EFC282C5 for ; Mon, 3 Mar 2025 12:57:28 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DC40C6B0083; Mon, 3 Mar 2025 07:57:27 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id D73F2280001; Mon, 3 Mar 2025 07:57:27 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BEE3E6B008C; Mon, 3 Mar 2025 07:57:27 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id A0DB66B0083 for ; Mon, 3 Mar 2025 07:57:27 -0500 (EST) Received: from smtpin21.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id DB166514D4 for ; Mon, 3 Mar 2025 12:57:26 +0000 (UTC) X-FDA: 83180240892.21.229F4B5 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf04.hostedemail.com (Postfix) with ESMTP id 875A040007 for ; Mon, 3 Mar 2025 12:57:24 +0000 (UTC) Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=V+hWH61G; spf=pass (imf04.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1741006644; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=ZbBY5HPs9/ORp5FjR/nRtWeFfyn4LQ+KsSmcov6oEIs=; b=HKx7J7HQTuZs2lBI3yaW/N25Ah8YlxberaLPK/2D8scg5hvRGAPf/2zL09CAvI6aiq1gaZ DIFti2B6O+zeF3nXi7VIHeT6nK+2pJqDWt5YUNMw5w9RhjmPPgzqbVUpmsBOUvagrEowVq BNOQ+2jaNsGq5ZGRyB5i8ehLpoOjF3c= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=V+hWH61G; spf=pass (imf04.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1741006644; a=rsa-sha256; cv=none; b=KQG0KeXR5EdDKjroMYZ/DA4jzHM1FOiNXLUJaC+Pc1/PY10I12NP+fhMcpdQk5dT4uOqkx 2j2QxADTdzUHQAoERANes+M1Fn8i+ItJCTy3Zuo2pX194obaRjFZBS/HnUeV9VNNPnfEt/ FlmqCSA6ej/lF30N9R0nOnnuPZIlGP0= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1741006643; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=ZbBY5HPs9/ORp5FjR/nRtWeFfyn4LQ+KsSmcov6oEIs=; b=V+hWH61Gx+13/zGr/7lNqGpacjLdik0NXL+WzyTkxppgWdEYE8TiMiqHC2oNemegMyfbPZ vT4AwZSw40FeicjUndWMc3O+sj6zhby/TBU6SJ1VYTI+/sugVJPumFlYHWbaSKVVKEppoD eGTXC+U1I3xMDnjEiLoqBLsQTjvz8gc= Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-643-MkhD1SnCPQyYZv5nmYgbig-1; Mon, 03 Mar 2025 07:57:17 -0500 X-MC-Unique: MkhD1SnCPQyYZv5nmYgbig-1 X-Mimecast-MFC-AGG-ID: MkhD1SnCPQyYZv5nmYgbig_1741006636 Received: by mail-wr1-f72.google.com with SMTP id ffacd0b85a97d-390eefb2913so1883014f8f.0 for ; Mon, 03 Mar 2025 04:57:17 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1741006636; x=1741611436; h=content-transfer-encoding:in-reply-to:organization:autocrypt :content-language:from:references:cc:to:subject:user-agent :mime-version:date:message-id:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to; bh=ZbBY5HPs9/ORp5FjR/nRtWeFfyn4LQ+KsSmcov6oEIs=; b=cOCHaXsj2X+Jcs45kbi/9jSNMxKT+SfcWCfeQgf2GmCJbmEG1K631GtEWPe6DqYZrg Z97u2gdaVOj6WW4jW0RXj4fE8cAbPUEghiUt+MpkGlSo4UhL3vaJH9LyuTRR4Hz11Twd KVYBLS2mIc7GY3ORsMfIHjbWpSU7aD1UGjZMwrfqgCGOKaX0P6Ty/taVKCyQaB1y9DrI pxq+WUK2Cdbt86MVmzAKKy6pzA7slgeDUGgz0ZFMpbAdjSXdGDgCLo7/eSibsAOFffbw E3MQEPmcZrqRfGBl6js15HQBb1ybN2IBZSDYvnJA5jTbu/N2U3X8JRMxWkt3ZQoy1VeV xoVg== X-Gm-Message-State: AOJu0YykIuiXmSl+r3eYZxI15zqiGN7GdZ5WKiDAFCGUNp4cWKeCnR/A 11a6CT8UNdHVrxi3PcLDRi9FmAV9qy4WV9c283DuOL1zcgmDO7qyYAJuqzzU8vHwTzyMOvfEXdu M4FEnb5CLHmc9WUnr8humgUv3hsyzL8klDVzT8cOpBVyKaY+R X-Gm-Gg: ASbGnctZwVTuBozRKtxI0v56Y3Z9BI80JJhNUXOh6BgDsXNoKPSE0B5C/dmiLSlP8HK 1zGbl9ucXYjB6+bjROetuTegt8+SCleyOCXmM4om9sskBnOkK+M0hsXMakZkWs08tYwd802+KMl F8wYrsYwp5QksZAR/B+63ejP+hG0A+AyRpf2bff1UdOBqk9UEse9k8KTBGfTvLaVEcuuy6CPWX3 nv4IInyE/nLAuGq0GhddHm2nQHNgeKUERuGJ51HCiAtbyhwr+Xq6+XlJHQP9NlA/lVm+o7a7yME ZRSfebyMQbzzMZBKoy+ZmH3+od0RKkPCofmClLGxbC0yaejLoB0HHnkAoS4NzpPovd1qsPeHqAT 2bjcgspYgW14M1n/aB3fV8LpGeC0RswtG/UUQrtTsu9I= X-Received: by 2002:a05:6000:1568:b0:390:f6aa:4e7c with SMTP id ffacd0b85a97d-390f6aa506dmr8548951f8f.28.1741006636471; Mon, 03 Mar 2025 04:57:16 -0800 (PST) X-Google-Smtp-Source: AGHT+IGt3HqyWX69UNDm73XEavs4Jp5ikaGr7A82bFQLZfzfQ+Yf4WqMH1KFtPhi3+sLuqezP58sLw== X-Received: by 2002:a05:6000:1568:b0:390:f6aa:4e7c with SMTP id ffacd0b85a97d-390f6aa506dmr8548914f8f.28.1741006636083; Mon, 03 Mar 2025 04:57:16 -0800 (PST) Received: from ?IPV6:2003:cb:c734:9600:af27:4326:a216:2bfb? (p200300cbc7349600af274326a2162bfb.dip0.t-ipconnect.de. [2003:cb:c734:9600:af27:4326:a216:2bfb]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43aba58720esm192864235e9.40.2025.03.03.04.57.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 03 Mar 2025 04:57:15 -0800 (PST) Message-ID: <1fc8281b-72a2-454f-88dc-288084482cec@redhat.com> Date: Mon, 3 Mar 2025 13:57:14 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 4/4] Revert "x86/xen: allow nesting of same lazy mode" To: Ryan Roberts , Andrew Morton , "David S. Miller" , Andreas Larsson , Juergen Gross , Boris Ostrovsky , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , "Matthew Wilcox (Oracle)" , Catalin Marinas Cc: linux-mm@kvack.org, sparclinux@vger.kernel.org, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org References: <20250302145555.3236789-1-ryan.roberts@arm.com> <20250302145555.3236789-5-ryan.roberts@arm.com> <75031fe1-50d7-48d0-87bb-9c5c88f3b41c@redhat.com> <8b218b95-f0e3-424c-815f-5131e3e54031@arm.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <8b218b95-f0e3-424c-815f-5131e3e54031@arm.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: CGryiZ6d4BFqFMPvitn6MwKiNZrYfEyyr9pdMKDSS2E_1741006636 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: kwchs9e3uf31z73egh74g3wktiub4w31 X-Rspamd-Queue-Id: 875A040007 X-Rspamd-Server: rspam06 X-Rspam-User: X-HE-Tag: 1741006644-186187 X-HE-Meta: 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 /K1FcJqT RcOHe+6lByNFlgRupAAt9Wyi/WgiuVsJOrmeKBwfbIqVmQnd0LRsU2a95yLXA8t089grpe3fkMg6sMGgkDIJw+N5pfZBWTCB9EpIxQtIO0qf3CzpwCJ60se8RVpknEQotq6W0jYiywxaEx8h8AADwjpP6I1GB0p8Dcti653dIi+rdE7WcnkA6b3ABMSFePlY6p+j218jx/r5Iga8Kt9grwVkQTnA7xGslsbapyl4iAhLBxTGiMiUalsaQmRLU8cXSRSWUxLXME7EqdNegaTxlRhPFo9U1tm/S7/5bf1OSI5vKYUkcawbpCK2tPfNJdU1o07e813Wl9rDlDsMSWBKGd2mtsT/OdwOCiYoTerWTCiqBdNCKNrOo2EW5RHUrObzRxq+L2u8O4aYHLLU= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 03.03.25 13:33, Ryan Roberts wrote: > On 03/03/2025 11:52, David Hildenbrand wrote: >> On 02.03.25 15:55, Ryan Roberts wrote: >>> Commit 49147beb0ccb ("x86/xen: allow nesting of same lazy mode") was >>> added as a solution for a core-mm code change where >>> arch_[enter|leave]_lazy_mmu_mode() started to be called in a nested >>> manner; see commit bcc6cc832573 ("mm: add default definition of >>> set_ptes()"). >>> >>> However, now that we have fixed the API to avoid nesting, we no longer >>> need this capability in the x86 implementation. >>> >>> Additionally, from code review, I don't believe the fix was ever robust >>> in the case of preemption occurring while in the nested lazy mode. The >>> implementation usually deals with preemption by calling >>> arch_leave_lazy_mmu_mode() from xen_start_context_switch() for the >>> outgoing task if we are in the lazy mmu mode. Then in >>> xen_end_context_switch(), it restarts the lazy mode by calling >>> arch_enter_lazy_mmu_mode() for an incoming task that was in the lazy >>> mode when it was switched out. But arch_leave_lazy_mmu_mode() will only >>> unwind a single level of nesting. If we are in the double nest, then >>> it's not fully unwound and per-cpu variables are left in a bad state. >>> >>> So the correct solution is to remove the possibility of nesting from the >>> higher level (which has now been done) and remove this x86-specific >>> solution. >>> >>> Fixes: 49147beb0ccb ("x86/xen: allow nesting of same lazy mode") >> >> Does this patch here deserve this tag? IIUC, it's rather a cleanup now that it >> was properly fixed elsewhere. > > Now that nesting is not possible, yes it is just a cleanup. But when nesting was > possible, as far as I can tell it was buggy, as per my description. Right, I understood that part. > So it's a > bug bug that won't ever trigger once the other fixes are applied. Happy to > remove the Fixes and then not include it for stable for v2. That's probably > simplest. I was just curious, because it sounded like the actual fix was the other patch. Whatever you think is best :) -- Cheers, David / dhildenb