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 E6475D609D1 for ; Wed, 27 Nov 2024 10:51:31 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1tGFdH-0003Tc-Ev; Wed, 27 Nov 2024 05:50:55 -0500 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 1tGFdF-0003TB-C7 for qemu-devel@nongnu.org; Wed, 27 Nov 2024 05:50:53 -0500 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 1tGFdD-0007Fe-CR for qemu-devel@nongnu.org; Wed, 27 Nov 2024 05:50:53 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1732704649; 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=+uJWZ50LQAxYf1bSzKY1b4km2srzd5M5dS6SzCiNLWU=; b=dxhjSXBJqe+UB7/a+WOnwpxoBgqnzOu3h3Iosy9JvgPTctYZkf62ivO0ggCh66SLQSgWbz rIYqC0wCmWe8pRjIBvOckum6smMRtl8L/cAh1ElCh3N9QNBRugJT5j6ppakoixdEvy2ydL /TWuDLiBDp4HOgtJ0mZZjme3V9OgqDg= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-652-gfig3CsjNqqdE_X2z_Ta1g-1; Wed, 27 Nov 2024 05:50:48 -0500 X-MC-Unique: gfig3CsjNqqdE_X2z_Ta1g-1 X-Mimecast-MFC-AGG-ID: gfig3CsjNqqdE_X2z_Ta1g Received: by mail-wm1-f72.google.com with SMTP id 5b1f17b1804b1-434a90febb8so6805515e9.1 for ; Wed, 27 Nov 2024 02:50:48 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1732704647; x=1733309447; 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=+uJWZ50LQAxYf1bSzKY1b4km2srzd5M5dS6SzCiNLWU=; b=W6Uq+CnpZzd8Rozbmdg2FASuOsAh5N2J9YklrAck6xemeODiHcnFdJxV2noSsibihY 23e+FAx0qEY9ws/45lXxvW0s4xi3sxj0gVvUy42z7rsQ4iyE59bUBEp0gV9VBGwuWaJt 58v7FhaFHJQ3dPtg0QS+A/xIS6/1Zwum5I6V9ef1/V7ORzApN8AuF7HJd5zRUMgm0NA8 nBPFpfSotpLNUm1vJJUdpvwN9wVCdrcNGTZpXzNExPnIEFaCpPL8KxuWbfdzH0dYxi4V bZyi7PKVw5U9Firz00P1m8oz0vrOP/ikaq4jrLAAfw4LclUVG5w8XGiXiMVl7TmRWM/b liGQ== X-Gm-Message-State: AOJu0Yx+NKm6x7ubA2mQ+OpYBxY9y5FVxbxsFTjlHMXC2JL14KUxgX9P /OvCa2xVJvncAw2nkxvxXva4v18J6n/AeRWLn6gLqFsF/bBgCUxy6MYJe1o4Hmv3nw6A7OLF6wr CiJf3ZhJlE0zVPQMbBIvXeHc62rgMclRZR7hkXkPyztiFtEPgj5KP X-Gm-Gg: ASbGncuYQ4XvR7ZMMWF3YgkXaby+O4CVkzk+99Xcdyn9UxNLwg0XXDXEZT6GUYC6iuK er02wrdrqGyqDqd+v0yyrUee8rhb7xxtmjChJkuPp06pLYfdlQMPbs8LR/2km6UqowSr2cHxW/L tnrXuahCWYZ5UdDcXPhxoLmtnHGv5ynBhFYpZ6Qbb5dKZIc7YWsD/Jed8T/cNhb7k18mspbMwPy wK70CVz0+JhjVGSqHUqIfT0PdzlMvdxeJ0AQVnQVvJmZeZR+InZ8POElyYCFHaHjQQM1QBQwDKg 0pHPcqtLIZC1Ec5OSbEkxXjhbZR/wqTaqx2/yeXa80TybJ/Kcb0KsFgq3Qd1SJKRp2ZmzXbGPp8 aSQ== X-Received: by 2002:a05:600c:3ba6:b0:42c:ae30:fc4d with SMTP id 5b1f17b1804b1-434a9dbba7dmr22012625e9.7.1732704647280; Wed, 27 Nov 2024 02:50:47 -0800 (PST) X-Google-Smtp-Source: AGHT+IHEsixbQTnY05kVAjOjtF8R4yMZ3brnTkEswnFFGltLTsA6oa94DPVqce/Xc7YxFp0YrhOKKQ== X-Received: by 2002:a05:600c:3ba6:b0:42c:ae30:fc4d with SMTP id 5b1f17b1804b1-434a9dbba7dmr22012385e9.7.1732704646917; Wed, 27 Nov 2024 02:50:46 -0800 (PST) Received: from ?IPV6:2003:cb:c70d:be00:66fa:83a6:8803:977e? (p200300cbc70dbe0066fa83a68803977e.dip0.t-ipconnect.de. [2003:cb:c70d:be00:66fa:83a6:8803:977e]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-434aa74f1e6sm17491775e9.9.2024.11.27.02.50.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 27 Nov 2024 02:50:46 -0800 (PST) Message-ID: Date: Wed, 27 Nov 2024 11:50:45 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/5] vhost-user: Add VIRTIO Shared Memory map request To: Albert Esteve Cc: qemu-devel@nongnu.org, =?UTF-8?Q?Alex_Benn=C3=A9e?= , slp@redhat.com, hi@alyssa.is, mst@redhat.com, jasowang@redhat.com, stefanha@redhat.com, Stefano Garzarella , stevensd@chromium.org References: <20240912145335.129447-1-aesteve@redhat.com> <20240912145335.129447-2-aesteve@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: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, 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 >> RAM memory region/ RAMBlock that has properly set flags/fd/whatssoever >> and map whatever you want in there. >> >> Likely you would need a distinct RAMBlock/RAM memory region per mmap(), >> and would end up mmaping implicitly via qemu_ram_mmap(). >> >> Then, your shared region would simply be an empty container into which >> you map these RAM memory regions. > Hi, > Hi, sorry it took me so long to get back to this. Lately I have been > testing the patch and fixing bugs, and I am was going to add some > tests to be able to verify the patch without having to use a backend > (which is what I am doing right now). > > But I wanted to address/discuss this comment. I am not sure of the > actual problem with the current approach (I am not completely aware of > the concern in your first paragraph), but I see other instances where > qemu mmaps stuff into a MemoryRegion. I suggest you take a look at the three relevant MAP_FIXED users outside of user emulation code. (1) hw/vfio/helpers.c: We create a custom memory region + RAMBlock with memory_region_init_ram_device_ptr(). This doesn't mmap(MAP_FIXED) into any existing RAMBlock. (2) system/physmem.c: I suggest you take a close look at qemu_ram_remap() and how it is one example of how RAMBlock properties describe exactly what is mmaped. (3) util/mmap-alloc.c: Well, this is the code that performs the mmap(), to bring a RAMBlock to life. See qemu_ram_mmap(). There is some oddity hw/xen/xen-mapcache.c; XEN mapcache seems to manage guest RAM without RAMBlocks. > Take into account that the > implementation follows the definition of shared memory region here: > https://docs.oasis-open.org/virtio/virtio/v1.3/csd01/virtio-v1.3-csd01.html#x1-10200010 > Which hints to a memory region per ID, not one per required map. So > the current strategy seems to fit it better. I'm confused, we are talking about an implementation detail here? How is that related to the spec? > > Also, I was aware that I was not the first one attempting this, so I > based this code in previous attempts (maybe I should give credit in > the commit now that I think of): > https://gitlab.com/virtio-fs/qemu/-/blob/qemu5.0-virtiofs-dax/hw/virtio/vhost-user-fs.c?ref_type=heads#L75 > As you can see, it pretty much follows the same strategy. So, people did some hacky things in a QEMU fork 6 years ago ... :) That cannot possibly be a good argument why we should have it like that in QEMU. > And in my > examples I have been able to use this to video stream with multiple > queues mapped into the shared memory (used to capture video frames), > using the backend I mentioned above for testing. So the concept works. > I may be wrong with this, but for what I understood looking at the > code, crosvm uses a similar strategy. Reserve a memory block and use > for all your mappings, and use an allocator to find a free slot. > Again, I suggest you take a look at what a RAMBlock is, and how it's properties describe the containing mmap(). > And if I were to do what you say, those distinct RAMBlocks should be > created when the device starts? What would be their size? Should I > create them when qemu receives a request to mmap? How would the driver > find the RAMBlock? You'd have an empty memory region container into which you will map memory regions that describe the memory you want to share. mr = g_new0(MemoryRegion, 1); memory_region_init(mr, OBJECT(TODO), "vhost-user-shm", region_size); Assuming you are requested to mmap an fd, you'd create a new MemoryRegion+RAMBlock that describes the memory and performs the mmap() for you: map_mr = g_new0(MemoryRegion, 1); memory_region_init_ram_from_fd(map_mr, OBJECT(TODO), "TODO", map_size, RAM_SHARED, map_fd, map_offs, errp); To then map it into your container: memory_region_add_subregion(mr, offset_within_container, map_mr); To unmap, you'd first remove the subregion, to then unref the map_mr. The only alternative would be to do it like (1) above: you perform all of the mmap() yourself, and create it using memory_region_init_ram_device_ptr(). This will set RAM_PREALLOC on the RAMBlock and tell QEMU "this is special, just disregard it". The bad thing about RAM_PREALLOC will be that it will not be compatible with vfio, not communicated to other vhost-user devices etc ... whereby what I describe above would just work with them. -- Cheers, David / dhildenb