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 8945FE7717F for ; Tue, 10 Dec 2024 19:48:50 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id D5C8D6B016C; Tue, 10 Dec 2024 14:48:49 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id D0D276B0170; Tue, 10 Dec 2024 14:48:49 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B5FB86B0172; Tue, 10 Dec 2024 14:48:49 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 959AB6B016C for ; Tue, 10 Dec 2024 14:48:49 -0500 (EST) Received: from smtpin12.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 36F46AECA4 for ; Tue, 10 Dec 2024 19:48:49 +0000 (UTC) X-FDA: 82880086548.12.7C27C1D Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf04.hostedemail.com (Postfix) with ESMTP id 249C34001A for ; Tue, 10 Dec 2024 19:48:23 +0000 (UTC) Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=iCL2qR63; spf=pass (imf04.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 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=1733860104; 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=DMcsbtd5lFCfZcI6bs5zJZ1evSaPUcT7e2jE51rdWGc=; b=qqd1q5Yl+T7CJf/cQneelHO7bRilyp0RHJh2VbmC2AdUezDspHPTfXQg+KJEezSATSiPiv nmfVWxOa9mMAzdJBvOQR4sUM+D6017WorZxzs6WZ+pzsLmxptt/6t/a+9vcxxs8evSOzJ9 MRe5hvPc4/QkOWCbTHYPsvzQrazan3Q= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1733860104; a=rsa-sha256; cv=none; b=t8dbwGfM4EVyy2Mzc3ei3Z8+iSEBwDf7P1usze9ZUyvaCy5ITR+6i9jmc/+qpvzQaZGsTv oJzjTEY+uYbEH15EEMCODE6K5pyx16uwWjgkpfsn9pWQZW1ySjhZxzFKAOU6/NBTn1IEKH MLcUqTZaaSWGooXNcLxMMH5KGMGX+dc= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=iCL2qR63; spf=pass (imf04.hostedemail.com: domain of david@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1733860126; 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=DMcsbtd5lFCfZcI6bs5zJZ1evSaPUcT7e2jE51rdWGc=; b=iCL2qR63vvTdcAcmoEHzof5OKMTqcJlqgIDIkuFtnSep6mIKYiPgdSTZy9VBHrf3WMqvZt l41A0xafIUSfLgZxb8cY+MLktoenxEFnabyOdR0eOGujpnfL0QBwZbJ9GXXNzqm/AskoYH n4NLPiVqL6NraOAlI9Ef2SaFtE5uySM= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-504-rSOdmsimPTebvcNEBvOwyw-1; Tue, 10 Dec 2024 14:48:44 -0500 X-MC-Unique: rSOdmsimPTebvcNEBvOwyw-1 X-Mimecast-MFC-AGG-ID: rSOdmsimPTebvcNEBvOwyw Received: by mail-wm1-f70.google.com with SMTP id 5b1f17b1804b1-43619b135bcso3863555e9.1 for ; Tue, 10 Dec 2024 11:48:44 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1733860123; x=1734464923; 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=DMcsbtd5lFCfZcI6bs5zJZ1evSaPUcT7e2jE51rdWGc=; b=P2J/Wi/9EksBarodfT2/vLBn+taG+54IvxBjPpMDyukjou9yetc28Nd9QciBwSQW5D geqd/po50uJzn3n0ucCqkEGt+29G0dEnzRKBDaZ4ChPf+D6j1MUdFICIIEeQ76UsGuL/ edkoxN9pF9TJ2JJDbYXphSlCVaxzniqV50Q9RFlGASZhvpmTs/jub2Lt4izjaxywIlJU G6yaB9TX/zjNQDNMiucGUnZy4k0EFEwM6MIG3T7cqoo2bu1hzSQeKXvdv8LXr3idJQvp 7TZ0L8nb8o4E2Cv8c94VmbaS0UppcplYonVh2/xZc4Iz2WIZjgYR/q+vAXqpDuNYumgl o/Pw== X-Forwarded-Encrypted: i=1; AJvYcCUFE7igHozNjBD4GRtgfTB+vAaN6I+N3LVkTqOSZ21nnniJYBjg8eQuM6rIizPr48csXrJBOmzgaQ==@kvack.org X-Gm-Message-State: AOJu0Yx/LYYX3y03zG4pMvEvzt/31XBjOftwCTVTdDKRQuBCYiUDoDSj OxQqv2ig3cFUraYzST/NOfmP8qcup76EKT8osrQg0AhKsZf5KP6zyzxshpy2aOyl7o1r7rdnjFm C7pXKa/ke6bdrUb2pOqeDlKHmYj9kZsR366J/2u6MKufYPQ8Ds0cQG9X5Yk8= X-Gm-Gg: ASbGncv8nNzb2HpbA6X8JX+NScyIzi33vycc0wCEz0lWM15jknianC+6XpW3g3+Cq5+ 8lA05kgeh+OI0fKuaFmfSSwX8VlXvfnSKEr3YmL4UTzfr9QKO1UCYVtpAIJ9+c26ZR1XSMvnI+W +4pjqidL+Jb3Brf4bZzV6i1tk1JKVcVHWRByduT6fDWza/PziM/0ySUHjQXCNjS8MkV6rlypl9M 3r+JVBc61y+3EHKTZEOEgpJCx141jZS9qGWXxskHDDejwDEVaj3NflL3rG57u61zZJ35+qouVG/ 6aG9jtY= X-Received: by 2002:a05:600c:cc7:b0:435:194:3cdf with SMTP id 5b1f17b1804b1-4361c3a3055mr639625e9.19.1733860123447; Tue, 10 Dec 2024 11:48:43 -0800 (PST) X-Google-Smtp-Source: AGHT+IGd1aJL+x+TohxMkH85BPdM7N12C0P/wEJqAKFzcSCNqIeWNLDBcj+UUy2lKhJ5EDjEUHtNOw== X-Received: by 2002:a05:600c:cc7:b0:435:194:3cdf with SMTP id 5b1f17b1804b1-4361c3a3055mr639475e9.19.1733860123074; Tue, 10 Dec 2024 11:48:43 -0800 (PST) Received: from [192.168.3.141] (p5b0c61ad.dip0.t-ipconnect.de. [91.12.97.173]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-434f063357csm119151795e9.22.2024.12.10.11.48.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 10 Dec 2024 11:48:41 -0800 (PST) Message-ID: <405cc972-05c0-428a-afec-801ae4486ccb@redhat.com> Date: Tue, 10 Dec 2024 20:48:40 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: Mapping vmalloc pages to userspace To: Matthew Wilcox , linux-mm@kvack.org Cc: Uladzislau Rezki , Christoph Hellwig References: 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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: IxmbuOVcUcpoF6iTebM3ccZcULb-NTyTXMnkT5Py_ow_1733860123 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 249C34001A X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: 1mzisqrusshwsrmgyb7j9yh3jss5gjf9 X-HE-Tag: 1733860103-429685 X-HE-Meta: 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 pF47FTjH /+9k3vT88Zoq5P4Fy/wD0CuNc170qQEg4Ch4vBy3CEesNvW/uXJz3Ecq3WxajOjJssWIvWxzYmRYCQFggGYUvjn/f3XFExcyKATfKFBX2NGX2TSPJ7CbwgFCkd4ocz6skmDpGQv0uFtvojFmsY50xbs5tcv48XqiQ0HTIY1CIoeoj8Zj3nE78r0cAEZg6NpQQETKQeUcgDntmQx9Mn9BvpSplEel1vE+HOWebDT+xQ8omUzP2mCEkzWDrD8qT4fPxz3u8cbvcUpF/4YKBSAu9vYyHFRGb1MDwshV0HmMU50s9UMzlph1Bdv6IQm8iGx92ZsyOMy1i8NnDu7S9EsdMzVD1KAqwfarJpWXdf5Q3tDoYaoKvNjyxMuTorOeWnB28Psy8SX4uwkNfgj6MjxYgxiVT0Kr07QnMy/7j X-Bogosity: Ham, tests=bogofilter, spamicity=0.007865, 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 06.12.24 17:28, Matthew Wilcox wrote: Sorry for the late reply, interesting topic. > Today we have a very useful helper, remap_vmalloc_range() (and _partial()) > which lets drivers call vmalloc(), then map that memory to userspace. > It does so using vm_insert_page() which ends up calling folio_get() and > folio_add_file_rmap_pte(), so jiggling both the refcount and the mapcount. > > As you all know by now, we're looking to eliminate both mapcount and > refcount from struct page. I have four options for consideration, some > of which I like more than others. > > 1. We could introduce a vmalloc memdesc that has a per-page mapcount and > refcount. This seems like unnecessarily high overhead for a precision > of tracking that is, perhaps, not warranted. Especially the mapcount is probably of no use at all here. As discussed with Lorenzo recently, I assume we only perform this in vm_insert_page() because there is (was) no easy way to distinguish these pages on the zap path to *not* decrement the refcounts. With memdescs that would be easy (late: no folio -> no mapcount changes) > > 2. We could do no tracking at all of vmalloc pages. Insert the PFNs > of the allocated pages and rely on the driver to track everything > correctly, not freeing the vmalloc allocation until the mmap has been > torn down. This implies not supporting GUP. This option feels risky to > me; we're depending on device driver writers to get this right, and if > they get it wrong, it's quite the UAF hole; letting an attacker get > access to pages which could be allocated to any purpose. Fully agreed. > > 3. Embed a refcount into struct vm_struct. We can support GUP if we want. > Calling GUP bumps the refcount on the entire struct. When the refcount > hits zero, we free the entire allocation. There's no need for a mapcount > or pincount because we don't need to distinguish between temporary and > longterm gups. The pincount+mapcount should be specific to folios, agreed. > > 4. Introduce an indirection structure between the page and vm_struct which > contains the refcount. > > > I'm most in favour of #3, but there's probably ramifications I haven't > considered. I wonder if #1 only with the refcount would be doable. Maybe to a vmalloc memdesc, but a more generic kmem memdesc. Because for "oridnary" pages that a driver allocated I suspect we might want to do the same. But #3 sounds interesting as well. In any case, we'll have to teach vm_normal_page() users that blindly assume that they get a folio, that they could get something different instead. Using memdescs for that sounds reasonable. -- Cheers, David / dhildenb