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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5AA20C67861 for ; Mon, 8 Apr 2024 08:03:38 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rtjyN-0007Sd-Nb; Mon, 08 Apr 2024 04:03:23 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rtjyM-0007SQ-Sv for qemu-devel@nongnu.org; Mon, 08 Apr 2024 04:03:22 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rtjyL-00066F-30 for qemu-devel@nongnu.org; Mon, 08 Apr 2024 04:03:22 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1712563400; 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=HRzLsfi9v+rpjtpL/7jh+kVG4wDkrGyRBaLm7mCfyV8=; b=RttZw2TP4swFiIgykerVDjETxthlok6VkVucp3ZH+D3bClHxXiZBrkYWdj2xWH/RxuvEb6 pr5I++B6pKt38Vq1rbAKrh/u+8vxAlKKbo3fu3xHzvC0cpo5Gkb7DeUHNLSmSTKBxiX8dl PtEU4gTHKZRyJug88YeTymFgVtowLKU= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-436-_4KSeHxrOrqClpYwuKMI2w-1; Mon, 08 Apr 2024 04:03:18 -0400 X-MC-Unique: _4KSeHxrOrqClpYwuKMI2w-1 Received: by mail-wr1-f69.google.com with SMTP id ffacd0b85a97d-343c8e87a74so2494226f8f.0 for ; Mon, 08 Apr 2024 01:03:18 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1712563397; x=1713168197; 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=HRzLsfi9v+rpjtpL/7jh+kVG4wDkrGyRBaLm7mCfyV8=; b=NkXa9bFt4dkDZTs+vt5dXSWC8ey4bEfasxrKis5ntHusBnTe71oZeVkyTy4JR33p4c Me5H/UNbm/S3p+Wt19OsmrJ5oQqth+7cIiH4J/RSizncwzptxnU6hDnzmGtUBpx7hBze oFZx7MO/hMHO9JeY4vE3heTSmHT3JbchNfbzgcoTM/qvapG6s0O6rVU7nev3jo1k727e olgnMDHujEKnOMwrKIPDy67sK1z4J1rWkjJJLpIlLFQ9ik32yMNakfuH9/NqxHWEs8DB vRDWSpnk5OXI+2rb6yxQSlk2HuwZHQlx6AYl9kIJ+HZYmyO0X91nbVIX3yo8Uyf+eDXC XV5Q== X-Gm-Message-State: AOJu0YwLft/jLVeFa2d3FGHjmF/F+oQZvjnFypzwuY/gl6X7LpLx3Ljw p1+pBsMcXjzOZqIfKZ6zA54ZHkiYtByTt4pHth67vBxD2dOS/bBachYJeziKQkuzAot9CNU3Qf5 sHEGKn9HKIiXpGVyy+X+sK0ntQ/tyFgTuhotuKWEesXbt6MMWus+x X-Received: by 2002:a05:6000:152:b0:343:96a0:cccd with SMTP id r18-20020a056000015200b0034396a0cccdmr7142030wrx.33.1712563397243; Mon, 08 Apr 2024 01:03:17 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHb1/5jeKgCie52fRfsLM7Timc6gB3AiDcGwJHGBHA4WYzy58wbGemoZcZTvfOH+ghT2erXxg== X-Received: by 2002:a05:6000:152:b0:343:96a0:cccd with SMTP id r18-20020a056000015200b0034396a0cccdmr7141996wrx.33.1712563396812; Mon, 08 Apr 2024 01:03:16 -0700 (PDT) Received: from ?IPV6:2003:cb:c718:1300:9860:66a2:fe4d:c379? (p200300cbc7181300986066a2fe4dc379.dip0.t-ipconnect.de. [2003:cb:c718:1300:9860:66a2:fe4d:c379]) by smtp.gmail.com with ESMTPSA id dr20-20020a5d5f94000000b0033ea499c645sm8455913wrb.4.2024.04.08.01.03.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 08 Apr 2024 01:03:16 -0700 (PDT) Message-ID: Date: Mon, 8 Apr 2024 10:03:15 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH for-9.1 v3 09/11] hostmem: add a new memory backend based on POSIX shm_open() To: Stefano Garzarella Cc: qemu-devel@nongnu.org, Coiby Xu , "Michael S. Tsirkin" , qemu-block@nongnu.org, =?UTF-8?Q?Daniel_P=2E_Berrang=C3=A9?= , slp@redhat.com, Eduardo Habkost , Kevin Wolf , Hanna Reitz , Igor Mammedov , =?UTF-8?Q?Marc-Andr=C3=A9_Lureau?= , Thomas Huth , Raphael Norwitz , =?UTF-8?Q?Philippe_Mathieu-Daud=C3=A9?= , Brad Smith , stefanha@redhat.com, Eric Blake , Paolo Bonzini , Laurent Vivier , Markus Armbruster , gmaglione@redhat.com, Jason Wang References: <20240404122330.92710-1-sgarzare@redhat.com> <20240404122330.92710-10-sgarzare@redhat.com> From: David Hildenbrand Content-Language: en-US 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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -44 X-Spam_score: -4.5 X-Spam_bar: ---- X-Spam_report: (-4.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-2.355, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 08.04.24 09:58, Stefano Garzarella wrote: > On Thu, Apr 04, 2024 at 04:09:34PM +0200, David Hildenbrand wrote: >> On 04.04.24 14:23, Stefano Garzarella wrote: >>> shm_open() creates and opens a new POSIX shared memory object. >>> A POSIX shared memory object allows creating memory backend with an >>> associated file descriptor that can be shared with external processes >>> (e.g. vhost-user). >>> >>> The new `memory-backend-shm` can be used as an alternative when >>> `memory-backend-memfd` is not available (Linux only), since shm_open() >>> should be provided by any POSIX-compliant operating system. >>> >>> This backend mimics memfd, allocating memory that is practically >>> anonymous. In theory shm_open() requires a name, but this is allocated >>> for a short time interval and shm_unlink() is called right after >>> shm_open(). After that, only fd is shared with external processes >>> (e.g., vhost-user) as if it were associated with anonymous memory. >>> >>> In the future we may also allow the user to specify the name to be >>> passed to shm_open(), but for now we keep the backend simple, mimicking >>> anonymous memory such as memfd. >>> >>> Signed-off-by: Stefano Garzarella >>> --- >>> v3 >>> - enriched commit message and documentation to highlight that we >>> want to mimic memfd (David) >>> --- >>> docs/system/devices/vhost-user.rst | 5 +- >>> qapi/qom.json | 17 +++++ >>> backends/hostmem-shm.c | 118 +++++++++++++++++++++++++++++ >>> backends/meson.build | 1 + >>> qemu-options.hx | 11 +++ >>> 5 files changed, 150 insertions(+), 2 deletions(-) >>> create mode 100644 backends/hostmem-shm.c >>> >>> diff --git a/docs/system/devices/vhost-user.rst b/docs/system/devices/vhost-user.rst >>> index 9b2da106ce..35259d8ec7 100644 >>> --- a/docs/system/devices/vhost-user.rst >>> +++ b/docs/system/devices/vhost-user.rst >>> @@ -98,8 +98,9 @@ Shared memory object >>> In order for the daemon to access the VirtIO queues to process the >>> requests it needs access to the guest's address space. This is >>> -achieved via the ``memory-backend-file`` or ``memory-backend-memfd`` >>> -objects. A reference to a file-descriptor which can access this object >>> +achieved via the ``memory-backend-file``, ``memory-backend-memfd``, or >>> +``memory-backend-shm`` objects. >>> +A reference to a file-descriptor which can access this object >>> will be passed via the socket as part of the protocol negotiation. >>> Currently the shared memory object needs to match the size of the main >>> diff --git a/qapi/qom.json b/qapi/qom.json >>> index 85e6b4f84a..5252ec69e3 100644 >>> --- a/qapi/qom.json >>> +++ b/qapi/qom.json >>> @@ -721,6 +721,19 @@ >>> '*hugetlbsize': 'size', >>> '*seal': 'bool' } } >>> +## >>> +# @MemoryBackendShmProperties: >>> +# >>> +# Properties for memory-backend-shm objects. >>> +# >>> +# The @share boolean option is true by default with shm. >>> +# >>> +# Since: 9.1 >>> +## >>> +{ 'struct': 'MemoryBackendShmProperties', >>> + 'base': 'MemoryBackendProperties', >>> + 'data': { } } >>> + >> >> Acked-by: David Hildenbrand >> >> One comment: we should maybe just forbid setting share=off. it doesn't >> make any sense and it can even result in an unexpected double memory >> consumption. We missed doing that for memfd, unfortunately. > > Good point! > > IIUC the `share` property is defined by the parent `hostmem`, so I > should find a way to override the property here and disable the setter, > or add an option to `hostmem` to make the property non-writable. Right, or simply fail later when you would find "share=off" in shm_backend_memory_alloc(). When ever supporting named shmem_open(), it could make sense for VM snapshotting. Right now it doesn't really make any sense. -- Cheers, David / dhildenb