From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yb1-f169.google.com (mail-yb1-f169.google.com [209.85.219.169]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 588C9158A09; Wed, 29 Jan 2025 19:40:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.219.169 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738179655; cv=none; b=E4Dl8aJPkMdZvmEbvUB61DPZHIGlAkNcLi+iuKumHRzTry1vq3MOnem5klLybZ0pCfmOw4QlonZwvwRnPAKdhwQ9sLFpxmxx9rJGSRsq3A0rdrlVnDKMSdWh8Z50ad1IDaW5R31s16+RYaU8viCO+x8JzLKQLLJvHsoqoBUGCdc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738179655; c=relaxed/simple; bh=n0qc7hxwmQT3LcE9Yl45QXnZe+KyfZkh3DIPJkcoiBs=; h=Message-ID:Date:MIME-Version:Subject:From:To:References: In-Reply-To:Content-Type; b=qnm0bInO91D6h9ehjTpug7tkdfOVKbaI4HMfPI12PQ6FLDwQGrb/H01rIBVFE1CqSrr0n39Yrtg1YsO/zmAY9OQ9yUnEc0N2BgylUOIyPlCyd2sJWClxJVFH8SE/IE0x47V51UibiMlhco6tSd0+TDfh6vJQrbshmkPzf+VNJfQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=kB7hYCUf; arc=none smtp.client-ip=209.85.219.169 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="kB7hYCUf" Received: by mail-yb1-f169.google.com with SMTP id 3f1490d57ef6-e58a99f493bso124323276.2; Wed, 29 Jan 2025 11:40:52 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1738179652; x=1738784452; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:autocrypt:content-language :references:to:from:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=YiAwe4ZwCv8Im80AYWWU2ZRBnO1Np7+D1TolCE4p/M0=; b=kB7hYCUfY+ypECLEXsKI/+DFPiqDESW2JesuehlY0WOSR0G8QJo+YHucRaoemX7pjy pS/HxJ9+uSTUHfj/u0BGBuboHOU5YLmvx33LH9aLCvjZFyo9uSaLc+E6t+9ouiUOyM3j 6gtYKxBGKafMXUFONa5ODQnZ27neRjr70C+hMJ61UghrSV2T1qr1RXlev2QemIlKDEdc 05aKhKGB0rZ3oFRurZiU+T8mcyMgMtX0cskZWdFP6ORSQ3T+zRel93rq5Xbskk8hMaey EufVcBmaAshahtl1CLMWf9+c6BEKm8cUb4RynqFvpNCHK1cMjIHx+z8cUmn76z0GUC5m jXIQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1738179652; x=1738784452; h=content-transfer-encoding:in-reply-to:autocrypt:content-language :references:to:from:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=YiAwe4ZwCv8Im80AYWWU2ZRBnO1Np7+D1TolCE4p/M0=; b=gMImY5cmQiCJgexEpMsTIZZLcGyC6Lps7MTkM19tt+QIJmA9Gi9VKWw6OWqUw4NXbD KeyS8W6IPdGnhBr4qAEDtDBG9HWYPtkiOiir+HFe+CxrFYWELyJbyo35soU1MVSY2H7c mYQ5loRMTd8+z+TVxbMHU1I22fz78jm8jdB0jrfj9PU6j5Pp1QgN7WyoskYWTadNT7Et QRC3SyryP0523wYFIFCAwxLE9MawDbkGdsJ5JiXp0mm+OQfoxZpkvgdnZvwykZTaqjli Qaw/Ud9VW9cUcXA5O53J8BVythe6ZhVAQTQRoxdH+25OhQcqBmrDOk2g05Uon9Tu8a7Y eNQQ== X-Forwarded-Encrypted: i=1; AJvYcCW0qB0HcXKR9VGljK3SCDUf12G1sMepFTWbRIMTeCzEVAG3/hfoediCQkHntRBWV/ztdr4=@vger.kernel.org, AJvYcCXMlNIIQYZ3UUntUurwg0T3DQcCdwCliltA9s9rAWRJHHvgkJBTR1XiMnDL3EoziEj47iMnXH6MVIV3YJIN@vger.kernel.org X-Gm-Message-State: AOJu0YzVd+yaOjiFYhGrl5pR751F6az3sHB0EpOIqwtVS3yPauwjqgiy mefcDhVV7rz0niswCIwxCHdpE3qgYTmIUhFaxrEKbmqabJkxSP4e X-Gm-Gg: ASbGncvrKyr7jhVCRPNuKEgNBL3Sc59A+Vib3tUyBWQQHxdFIxxaCotLOcG6oq/jlzW q7uQ4wzS7uT2WZZcUsP0pIDd5ZfxHUpIIBtM/7bjCW/kpOtIGM8zMV4BuR2orK3KIG+A5IRmP4M ULjEcQREraLqJGUvgjJOPe+UvOdnG8vorAa+G2poTXHrtrNVXgG9zY54f119ov5onU4UkaO9QxG MzeTla/iYF1adDUEZqw8N04y4qzZUCsUGOt/+6lfNHYddR0mA9QfQdYMLm18pIpVDGbKqCFevtB f2zNLW95/GvIwXuT/Mw= X-Google-Smtp-Source: AGHT+IFcm70cBzxdaG4YIpPTJqjr1mlkmvf4KaftoD5a2PQ8bLHewaoEFQM7aAbm4+WTw3yFJ6O+gg== X-Received: by 2002:a05:690c:4912:b0:6ef:805c:ea15 with SMTP id 00721157ae682-6f7a83fd04bmr32763617b3.23.1738179652005; Wed, 29 Jan 2025 11:40:52 -0800 (PST) Received: from [10.138.7.94] ([45.134.140.51]) by smtp.gmail.com with ESMTPSA id 00721157ae682-6f757a2ac24sm23937107b3.103.2025.01.29.11.40.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 29 Jan 2025 11:40:51 -0800 (PST) Message-ID: Date: Wed, 29 Jan 2025 14:40:50 -0500 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 3/3] drm/virtio: implement blob userptr resource object From: Demi Marie Obenour To: "Huang, Honglei1" , Huang Rui , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Dmitry Osipenko , dri-devel@lists.freedesktop.org, David Airlie , Gerd Hoffmann , Gurchetan Singh , Chia-I Wu , Akihiko Odaki , Lingshan Zhu , Simona Vetter , Xen developer discussion , Kernel KVM virtualization development , =?UTF-8?Q?Marek_Marczykowski-G=C3=B3recki?= References: <20241220100409.4007346-1-honglei1.huang@amd.com> <20241220100409.4007346-3-honglei1.huang@amd.com> <2fb36b50-4de2-4060-a4b7-54d221db8647@gmail.com> <9572ba57-5552-4543-a3b0-6097520a12a3@gmail.com> Content-Language: en-US Autocrypt: addr=demiobenour@gmail.com; keydata= xsFNBFp+A0oBEADffj6anl9/BHhUSxGTICeVl2tob7hPDdhHNgPR4C8xlYt5q49yB+l2nipd aq+4Gk6FZfqC825TKl7eRpUjMriwle4r3R0ydSIGcy4M6eb0IcxmuPYfbWpr/si88QKgyGSV Z7GeNW1UnzTdhYHuFlk8dBSmB1fzhEYEk0RcJqg4AKoq6/3/UorR+FaSuVwT7rqzGrTlscnT DlPWgRzrQ3jssesI7sZLm82E3pJSgaUoCdCOlL7MMPCJwI8JpPlBedRpe9tfVyfu3euTPLPx wcV3L/cfWPGSL4PofBtB8NUU6QwYiQ9Hzx4xOyn67zW73/G0Q2vPPRst8LBDqlxLjbtx/WLR 6h3nBc3eyuZ+q62HS1pJ5EvUT1vjyJ1ySrqtUXWQ4XlZyoEFUfpJxJoN0A9HCxmHGVckzTRl 5FMWo8TCniHynNXsBtDQbabt7aNEOaAJdE7to0AH3T/Bvwzcp0ZJtBk0EM6YeMLtotUut7h2 Bkg1b//r6bTBswMBXVJ5H44Qf0+eKeUg7whSC9qpYOzzrm7+0r9F5u3qF8ZTx55TJc2g656C 9a1P1MYVysLvkLvS4H+crmxA/i08Tc1h+x9RRvqba4lSzZ6/Tmt60DPM5Sc4R0nSm9BBff0N m0bSNRS8InXdO1Aq3362QKX2NOwcL5YaStwODNyZUqF7izjK4QARAQABzTxEZW1pIE1hcmll IE9iZW5vdXIgKGxvdmVyIG9mIGNvZGluZykgPGRlbWlvYmVub3VyQGdtYWlsLmNvbT7CwXgE EwECACIFAlp+A0oCGwMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJELKItV//nCLBhr8Q AK/xrb4wyi71xII2hkFBpT59ObLN+32FQT7R3lbZRjVFjc6yMUjOb1H/hJVxx+yo5gsSj5LS 9AwggioUSrcUKldfA/PKKai2mzTlUDxTcF3vKx6iMXKA6AqwAw4B57ZEJoMM6egm57TV19kz PMc879NV2nc6+elaKl+/kbVeD3qvBuEwsTe2Do3HAAdrfUG/j9erwIk6gha/Hp9yZlCnPTX+ VK+xifQqt8RtMqS5R/S8z0msJMI/ajNU03kFjOpqrYziv6OZLJ5cuKb3bZU5aoaRQRDzkFIR 6aqtFLTohTo20QywXwRa39uFaOT/0YMpNyel0kdOszFOykTEGI2u+kja35g9TkH90kkBTG+a EWttIht0Hy6YFmwjcAxisSakBuHnHuMSOiyRQLu43ej2+mDWgItLZ48Mu0C3IG1seeQDjEYP tqvyZ6bGkf2Vj+L6wLoLLIhRZxQOedqArIk/Sb2SzQYuxN44IDRt+3ZcDqsPppoKcxSyd1Ny 2tpvjYJXlfKmOYLhTWs8nwlAlSHX/c/jz/ywwf7eSvGknToo1Y0VpRtoxMaKW1nvH0OeCSVJ itfRP7YbiRVc2aNqWPCSgtqHAuVraBRbAFLKh9d2rKFB3BmynTUpc1BQLJP8+D5oNyb8Ts4x Xd3iV/uD8JLGJfYZIR7oGWFLP4uZ3tkneDfYzsFNBFp+A0oBEAC9ynZI9LU+uJkMeEJeJyQ/ 8VFkCJQPQZEsIGzOTlPnwvVna0AS86n2Z+rK7R/usYs5iJCZ55/JISWd8xD57ue0eB47bcJv VqGlObI2DEG8TwaW0O0duRhDgzMEL4t1KdRAepIESBEA/iPpI4gfUbVEIEQuqdqQyO4GAe+M kD0Hy5JH/0qgFmbaSegNTdQg5iqYjRZ3ttiswalql1/iSyv1WYeC1OAs+2BLOAT2NEggSiVO txEfgewsQtCWi8H1SoirakIfo45Hz0tk/Ad9ZWh2PvOGt97Ka85o4TLJxgJJqGEnqcFUZnJJ riwoaRIS8N2C8/nEM53jb1sH0gYddMU3QxY7dYNLIUrRKQeNkF30dK7V6JRH7pleRlf+wQcN fRAIUrNlatj9TxwivQrKnC9aIFFHEy/0mAgtrQShcMRmMgVlRoOA5B8RTulRLCmkafvwuhs6 dCxN0GNAORIVVFxjx9Vn7OqYPgwiofZ6SbEl0hgPyWBQvE85klFLZLoj7p+joDY1XNQztmfA rnJ9x+YV4igjWImINAZSlmEcYtd+xy3Li/8oeYDAqrsnrOjb+WvGhCykJk4urBog2LNtcyCj kTs7F+WeXGUo0NDhbd3Z6AyFfqeF7uJ3D5hlpX2nI9no/ugPrrTVoVZAgrrnNz0iZG2DVx46 x913pVKHl5mlYQARAQABwsFfBBgBAgAJBQJafgNKAhsMAAoJELKItV//nCLBwNIP/AiIHE8b oIqReFQyaMzxq6lE4YZCZNj65B/nkDOvodSiwfwjjVVE2V3iEzxMHbgyTCGA67+Bo/d5aQGj gn0TPtsGzelyQHipaUzEyrsceUGWYoKXYyVWKEfyh0cDfnd9diAm3VeNqchtcMpoehETH8fr RHnJdBcjf112PzQSdKC6kqU0Q196c4Vp5HDOQfNiDnTf7gZSj0BraHOByy9LEDCLhQiCmr+2 E0rW4tBtDAn2HkT9uf32ZGqJCn1O+2uVfFhGu6vPE5qkqrbSE8TG+03H8ecU2q50zgHWPdHM OBvy3EhzfAh2VmOSTcRK+tSUe/u3wdLRDPwv/DTzGI36Kgky9MsDC5gpIwNbOJP2G/q1wT1o Gkw4IXfWv2ufWiXqJ+k7HEi2N1sree7Dy9KBCqb+ca1vFhYPDJfhP75I/VnzHVssZ/rYZ9+5 1yDoUABoNdJNSGUYl+Yh9Pw9pE3Kt4EFzUlFZWbE4xKL/NPno+z4J9aWemLLszcYz/u3XnbO vUSQHSrmfOzX3cV4yfmjM5lewgSstoxGyTx2M8enslgdXhPthZlDnTnOT+C+OTsh8+m5tos8 HQjaPM01MKBiAqdPgksm1wu2DrrwUi6ChRVTUBcj6+/9IJ81H2P2gJk3Ls3AVIxIffLoY34E +MYSfkEjBz0E8CLOcAw7JIwAaeBT In-Reply-To: <9572ba57-5552-4543-a3b0-6097520a12a3@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 1/24/25 7:42 PM, Demi Marie Obenour wrote: > On 1/8/25 12:05 PM, Simona Vetter wrote: >> On Fri, Dec 27, 2024 at 10:24:29AM +0800, Huang, Honglei1 wrote: >>> >>> On 2024/12/22 9:59, Demi Marie Obenour wrote: >>>> On 12/20/24 10:35 AM, Simona Vetter wrote: >>>>> On Fri, Dec 20, 2024 at 06:04:09PM +0800, Honglei Huang wrote: >>>>>> From: Honglei Huang >>>>>> >>>>>> A virtio-gpu userptr is based on HMM notifier. >>>>>> Used for let host access guest userspace memory and >>>>>> notice the change of userspace memory. >>>>>> This series patches are in very beginning state, >>>>>> User space are pinned currently to ensure the host >>>>>> device memory operations are correct. >>>>>> The free and unmap operations for userspace can be >>>>>> handled by MMU notifier this is a simple and basice >>>>>> SVM feature for this series patches. >>>>>> The physical PFNS update operations is splited into >>>>>> two OPs in here. The evicted memories won't be used >>>>>> anymore but remap into host again to achieve same >>>>>> effect with hmm_rang_fault. >>>>> >>>>> So in my opinion there are two ways to implement userptr that make sense: >>>>> >>>>> - pinned userptr with pin_user_pages(FOLL_LONGTERM). there is not mmu >>>>> notifier >>>>> >>>>> - unpinnned userptr where you entirely rely on userptr and do not hold any >>>>> page references or page pins at all, for full SVM integration. This >>>>> should use hmm_range_fault ideally, since that's the version that >>>>> doesn't ever grab any page reference pins. >>>>> >>>>> All the in-between variants are imo really bad hacks, whether they hold a >>>>> page reference or a temporary page pin (which seems to be what you're >>>>> doing here). In much older kernels there was some justification for them, >>>>> because strange stuff happened over fork(), but with FOLL_LONGTERM this is >>>>> now all sorted out. So there's really only fully pinned, or true svm left >>>>> as clean design choices imo. >>>>> >>>>> With that background, why does pin_user_pages(FOLL_LONGTERM) not work for >>>>> you? >>>> >>>> +1 on using FOLL_LONGTERM. Fully dynamic memory management has a huge cost >>>> in complexity that pinning everything avoids. Furthermore, this avoids the >>>> host having to take action in response to guest memory reclaim requests. >>>> This avoids additional complexity (and thus attack surface) on the host side. >>>> Furthermore, since this is for ROCm and not for graphics, I am less concerned >>>> about supporting systems that require swappable GPU VRAM. >>> >>> Hi Sima and Demi, >>> >>> I totally agree the flag FOLL_LONGTERM is needed, I will add it in next >>> version. >>> >>> And for the first pin variants implementation, the MMU notifier is also >>> needed I think.Cause the userptr feature in UMD generally used like this: >>> the registering of userptr always is explicitly invoked by user code like >>> "registerMemoryToGPU(userptrAddr, ...)", but for the userptr release/free, >>> there is no explicit API for it, at least in hsakmt/KFD stack. User just >>> need call system call "free(userptrAddr)", then kernel driver will release >>> the userptr by MMU notifier callback.Virtio-GPU has no other way to know if >>> user has been free the userptr except for MMU notifior.And in UMD theres is >>> no way to get the free() operation is invoked by user.The only way is use >>> MMU notifier in virtio-GPU driver and free the corresponding data in host by >>> some virtio CMDs as far as I can see. >>> >>> And for the second way that is use hmm_range_fault, there is a predictable >>> issues as far as I can see, at least in hsakmt/KFD stack. That is the memory >>> may migrate when GPU/device is working. In bare metal, when memory is >>> migrating KFD driver will pause the compute work of the device in >>> mmap_wirte_lock then use hmm_range_fault to remap the migrated/evicted >>> memories to GPU then restore the compute work of device to ensure the >>> correction of the data. But in virtio-GPU driver the migration happen in >>> guest kernel, the evict mmu notifier callback happens in guest, a virtio CMD >>> can be used for notify host but as lack of mmap_write_lock protection in >>> host kernel, host will hold invalid data for a short period of time, this >>> may lead to some issues. And it is hard to fix as far as I can see. >>> >>> I will extract some APIs into helper according to your request, and I will >>> refactor the whole userptr implementation, use some callbacks in page >>> getting path, let the pin method and hmm_range_fault can be choiced >>> in this series patches. >> >> Ok, so if this is for svm, then you need full blast hmm, or the semantics >> are buggy. You cannot fake svm with pin(FOLL_LONGTERM) userptr, this does >> not work. > > Is this still broken in the virtualized case? Page migration between host > and device memory is completely transparent to the guest kernel, so pinning > guest memory doesn't interfere with the host KMD at all. In fact, the host > KMD is not even aware of it. To elaborate further: Memory in a KVM guest is *not* host physical memory, or even host kernel memory. It is host *userspace* memory, and in particular, *it is fully pageable*. There *might* be a few exceptions involving structures that are accessed by the (physical) CPU, but none of these are relevant here. This means that memory management works very differently than in the non-virtualized case. The host KMD can migrate pages between host memory and device memory without either the guest kernel or host userspace being aware that such migration has happened. This means that pin(FOLL_LONGTERM) in the guest doesn't pin memory on the host. Instead, it pins memory in the *guest*. The host will continue to migrate pages between host and device as needed. I’m no expert on SVM, but I suspect this is the desired behavior. Xen is significantly trickier, because most guest memory is provided by the Xen toolstack via the hypervisor and is _not_ pageable. Therefore, it cannot be mapped into the GPU without using Xen grant tables. Since Xen grants do not support non-cooperative revocation, this requires a FOLL_LONGTERM pin *anyway*. Furthermore, granted pages _cannot_ be migrated from host to device, so unless the GPU is an iGPU all of its accesses will need to cross the PCI bus. This will obviously be slow. The guest can avoid this problem by migrating userptr memory to virtio-GPU blob objects _before_ pinning it. Virtio-GPU blob objects are backed by host userspace memory, so the host can migrate them between device and host memory just like in the KVM case. Under KVM, such migration would be be slightly wasteful but otherwise harmless in the common case. In the case where PCI passthrough is also in use, however, it might be necessary even for KVM guests. This is because PCI passthrough requires pinned memory, and pinned memory cannot be migrated to the device. Since AMD’s automotive use-case uses Xen, and since KVM might also need page migration, I recommend that the initial implementation _always_ migrate pages to blob objects no matter what the hypervisor is. Direct GPU access to guest memory can be implemented as a KVM-specific optimization later. Also worth noting is that only pages that have been written need to be migrated. If a page hasn't been written, it should not be migrated, because unwritten pages of a blob objects will read as zero. However, the migration should almost certainly be done in 2M chunks, rather than 4K ones. This is because the TLBs of at least AMD GPU are optimized for 2M pages, and GPU access to 4K pages takes a 30% performance penalty. This nicely matches the penalty that AMD observed. -- Sincerely, Demi Marie Obenour (she/her/hers)