From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 019592FFDDB for ; Mon, 8 Sep 2025 15:50:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757346627; cv=none; b=eru9SXnk5IioOPwE3L2GnnoSRXI+zyqMLYa0qwnBRdAFDp7xkZTS+WB6vvCrTV4kBuMS57Do+tMZCmzKSPfS1zD0xkp1qj3K/edRq3RAn1cyOJfkLc1T0jXYtYdcWAS5v4Bd9drKLxVWc7hBaGczqq7l6mAiqf+4AB4Vihs9Fgs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757346627; c=relaxed/simple; bh=YOA9yiHHYWbHEuhKtxjwT6CMonYyVoporirKZbVud14=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=fHdfFmiZyK1p3thMNDDffXx94PZ5lzr1ccbjYb6Kiw8kEHd5d4EkwvDPXRZxDTaKgEChVZVdndtuAETzW0QsPUUEjjlUiQwJnFMeBxxUeUJPym698+j+gp/m9iYT/V9MqDvJWFLheN9VGgsqN6cBWimTqn9K66adLH8IRRSf5QY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=JJ9Ikt4h; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="JJ9Ikt4h" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1757346624; 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=yRW3ZVdYmN/Kdh0wLmiEq7GLlrJxKlfpeCG0COnVkik=; b=JJ9Ikt4hcQjosRnMCi/em3loNXCCoWr7kPV8y1aTnvueUHXG6SQZWZISPAFEjRaI8qaSbc vm4vTEuZVpBn1ZjN6Dd2f8bB7YHXRON5I+CJZ7ysqKxAzxErhZVpv3VhbsMx4KU2/jCNVs H1avd1/9c4PgaZp05euZoC4uHulLico= Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-452-9O2bcqsmPFSQLFzOWtKpDw-1; Mon, 08 Sep 2025 11:50:23 -0400 X-MC-Unique: 9O2bcqsmPFSQLFzOWtKpDw-1 X-Mimecast-MFC-AGG-ID: 9O2bcqsmPFSQLFzOWtKpDw_1757346622 Received: by mail-wm1-f71.google.com with SMTP id 5b1f17b1804b1-45dd66e1971so30647895e9.2 for ; Mon, 08 Sep 2025 08:50:23 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1757346622; x=1757951422; h=content-transfer-encoding:in-reply-to:autocrypt:content-language :references:cc:to:from:subject:user-agent:mime-version:date :message-id:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=yRW3ZVdYmN/Kdh0wLmiEq7GLlrJxKlfpeCG0COnVkik=; b=a2J+yF8cDy97LGSBNvcL61OSysJoZs9+oOt1wSygrmw3nItjfNb8Gbvl3jzl0TcgI/ 93rqayWGlphHPKnbv/xRA17oHsfZxNa7rbv0OmdxnpYBST8aFVBqrDcVT/QWMpWpSBM9 NhPLbHMNC7JPpx5xtaZd5Cec4QZyj3/aREuyBV+R/2G7v4EPiY7ArhidDmo4YsVt3cVd 9Jjlnzkl0z56/+LIYYzdSetdSHhhcp8+ovPmHYRpcRVX95J/LoiV4bs5pNNYy0K+eoO7 BTdarSIQlwUUtu3985W359GFpYNVRBOwxwzEB72FUnS92vGON/LhXsoYQo8PI5UTvV+h 3VzA== X-Forwarded-Encrypted: i=1; AJvYcCV2pJz4CtdIuxOlhXAiJG9MOd5TTZUU0EkiCq3ATpMdOssstFGvw3HOGkwhtl5TRBLPKDRYWNqKDNU=@vger.kernel.org X-Gm-Message-State: AOJu0Yy98J448g6vCMF3mI0pwUnn5zLtlT2eSsZjjLU5JSWv1DD86TAB fpqAqBJDD7AGoNphEETDE7a5c2QXwpBiWQBY3g7S5C/c+1n9fGeRCcnnJEPG6DYbciGnbw3j9xR UXTXfCJ9UJbwgrqDRMwroHPa4pMosI/Rit6+1Bz0Yj/w3xTYb7WeK37i7Rk1G4w== X-Gm-Gg: ASbGncvMEFd8Eqkc8w/JqVfZr+EhkprzWSvbpqW00SOJ0jNxUQVedWMcDaDd6zIR8Yt b2h/GCS/oAR4ry9F3XM6QzLaTGagiZSOtiZFKLUTpfvcO72RXcpy3y0eCGyTeQepe6LiKR/yKUL 3vqaog2DkJpFDsqWB30z3VekgLm8V7Y7GDBvhSci1tfWOJqyIYsQQmIZDoDufI+BcSgCfI3K2zf Ox6dhU35pwSmcxo+y1K2UXQSlSWatIe1A2EJtG56TFqeEMa9/W8Qw+9Ozp/0RbLHmOSB8/4513X EzyKL0kIeAaACC3bHNnvt5dd3c0orW6VSxxmEARETUAHOcmXWY4OewbDYtBnpYTSffcg9nAmKDA XgvsX6+wAIAp6S0L2crcY+w3trycU0Bbei+MxuNfNrmn33GBx2foEZHxUVxyihBAi X-Received: by 2002:a05:600c:4e14:b0:45b:86ee:415f with SMTP id 5b1f17b1804b1-45ddde8a741mr84356015e9.6.1757346622247; Mon, 08 Sep 2025 08:50:22 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEIS2Yy99pUw9GXFN0rA/K14GohJu1BEy0lmIZFIqwZ3w6bOX7inAYbi8cC2UvYQeQPJx4Tjw== X-Received: by 2002:a05:600c:4e14:b0:45b:86ee:415f with SMTP id 5b1f17b1804b1-45ddde8a741mr84355495e9.6.1757346621708; Mon, 08 Sep 2025 08:50:21 -0700 (PDT) Received: from ?IPV6:2003:d8:2f25:700:d846:15f3:6ca0:8029? (p200300d82f250700d84615f36ca08029.dip0.t-ipconnect.de. [2003:d8:2f25:700:d846:15f3:6ca0:8029]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45dd0595af9sm100737155e9.2.2025.09.08.08.50.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 08 Sep 2025 08:50:20 -0700 (PDT) Message-ID: <3229ac90-943f-4574-a9b8-bd4f5fa6cf03@redhat.com> Date: Mon, 8 Sep 2025 17:50:18 +0200 Precedence: bulk X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 03/16] mm: add vma_desc_size(), vma_desc_pages() helpers From: David Hildenbrand To: Jason Gunthorpe Cc: Lorenzo Stoakes , Andrew Morton , Jonathan Corbet , Matthew Wilcox , Guo Ren , Thomas Bogendoerfer , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , "David S . Miller" , Andreas Larsson , Arnd Bergmann , Greg Kroah-Hartman , Dan Williams , Vishal Verma , Dave Jiang , Nicolas Pitre , Muchun Song , Oscar Salvador , Konstantin Komarov , Baoquan He , Vivek Goyal , Dave Young , Tony Luck , Reinette Chatre , Dave Martin , James Morse , Alexander Viro , Christian Brauner , Jan Kara , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Hugh Dickins , Baolin Wang , Uladzislau Rezki , Dmitry Vyukov , Andrey Konovalov , Jann Horn , Pedro Falcato , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-csky@vger.kernel.org, linux-mips@vger.kernel.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, linux-mm@kvack.org, ntfs3@lists.linux.dev, kexec@lists.infradead.org, kasan-dev@googlegroups.com References: <20250908125101.GX616306@nvidia.com> <20250908133224.GE616306@nvidia.com> <090675bd-cb18-4148-967b-52cca452e07b@lucifer.local> <20250908142011.GK616306@nvidia.com> <764d413a-43a3-4be2-99c4-616cd8cd3998@lucifer.local> <20250908151637.GM616306@nvidia.com> <8edb13fc-e58d-4480-8c94-c321da0f4d8e@redhat.com> <20250908153342.GA789684@nvidia.com> <365c1ec2-cda6-4d94-895c-b2a795101857@redhat.com> 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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <365c1ec2-cda6-4d94-895c-b2a795101857@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: PzaQK_wBFgG85WPwAZmXEjjckISwWVFmZxreLukHGy4_1757346622 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 08.09.25 17:46, David Hildenbrand wrote: > On 08.09.25 17:33, Jason Gunthorpe wrote: >> On Mon, Sep 08, 2025 at 05:24:23PM +0200, David Hildenbrand wrote: >>>> >>>>> I think we need to be cautious of scope here :) I don't want to >>>>> accidentally break things this way. >>>> >>>> IMHO it is worth doing when you get into more driver places it is far >>>> more obvious why the VM_SHARED is being checked. >>>> >>>>> OK I think a sensible way forward - How about I add desc_is_cowable() or >>>>> vma_desc_cowable() and only set this if I'm confident it's correct? >>>> >>>> I'm thinking to call it vma_desc_never_cowable() as that is much much >>>> clear what the purpose is. >>> >>> Secretmem wants no private mappings. So we should check exactly that, not >>> whether we might have a cow mapping. >> >> secretmem is checking shared for a different reason than many other places.. > > I think many cases just don't want any private mappings. > > After all, you need a R/O file (VM_MAYWRITE cleared) mapped MAP_PRIVATE > to make is_cow_mapping() == false. Sorry, was confused there. R/O file does not matter with MAP_PRIVATE. I think we default to VM_MAYWRITE with MAP_PRIVATE unless someone explicitly clears it. So in practice there is indeed not a big difference between a private and cow mapping. -- Cheers David / dhildenb