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 gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (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 DCDB3E7719A for ; Wed, 8 Jan 2025 17:14:27 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 43FE510E8FC; Wed, 8 Jan 2025 17:14:27 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (1024-bit key; secure) header.d=ffwll.ch header.i=@ffwll.ch header.b="PstdYcgy"; dkim-atps=neutral Received: from mail-ej1-f44.google.com (mail-ej1-f44.google.com [209.85.218.44]) by gabe.freedesktop.org (Postfix) with ESMTPS id ABF3710E8FC for ; Wed, 8 Jan 2025 17:14:25 +0000 (UTC) Received: by mail-ej1-f44.google.com with SMTP id a640c23a62f3a-aaec61d0f65so12710166b.1 for ; Wed, 08 Jan 2025 09:14:25 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; t=1736356404; x=1736961204; darn=lists.freedesktop.org; h=in-reply-to:content-disposition:mime-version:references :mail-followup-to:message-id:subject:cc:to:from:date:from:to:cc :subject:date:message-id:reply-to; bh=rKvx99e6g4Z0rpqLB9wRUAqjWOH2T8CbRV87JKLyuz8=; b=PstdYcgypvcDY5HK+VNEV7QQ5Cbs6IfNVUBuXoDVTK1sVrONb4JRbGand9ZNEe/LFw 7/30DRFQUx7CKSzdSGh13tKyGML2P02frzqgHF3pQHs6SH2BLzM+ppsapqyhFJkEsli8 Myjda3b3jbpuDNXIYNlcfte9QM03WdTubuvFY= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1736356404; x=1736961204; h=in-reply-to:content-disposition:mime-version:references :mail-followup-to:message-id:subject:cc:to:from:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=rKvx99e6g4Z0rpqLB9wRUAqjWOH2T8CbRV87JKLyuz8=; b=h29eTPrbQuF9BU0sp/PHVwdptd00yGpOYDAc5nz9dJ9vrll5WPHiWR7UHzY8gnkoU6 3lWYw9xNrmf0fnObu6pAUicxtOKWtF/6xwz00dMKTkhqIHAIPZqBhedHCkY2rKzlMEx8 74bR5LcUEnmYuaozTtCxM/e5gQY+mNs5hV86Dg3T2RzdvCtDgSl10TLvDfNKII64Q4bm akuE+sU6O+fHGstLD3p5dRwCfC/C9l7MWzyq/+3S1HnQOksf34VYehRNfYPXCPop7by1 fV15gCMSyDcgS/qS+IXDZJcQnhU7/NUtYLlJDmXOKXhYL/txrFeBbAZmHoXbFGE2yzP0 ZTcA== X-Forwarded-Encrypted: i=1; AJvYcCX4RJAAx5GHHXxX84dT0F2/hwteqZdPgu+KhtvVgXQEHs7lrZpdK7wfNVcjGZSxmVI18ftLiux3Xrg=@lists.freedesktop.org X-Gm-Message-State: AOJu0YwsR/8j1Pw+/DpVeqp9YAiKqpiwIgN0jl8L38N7YBfUz/7EF/Vj 62J2vU0ZNnqIQVjTlwyYXmKQRegOsrpxVbfYkMRbEwchwOCgeTQeG7+NOYUq3LxswvGHygyleFt Y X-Gm-Gg: ASbGncu9iH6IuhpxXM/P5fjW+kpYEFca7pkFpm1p2z/VlNqsQg+onF2fWTdlFaDoE/n q9lMyhoPHFZFWuTX8zjQyo594eFW6xO9JUBudJFqcEhQ5ymeBCRpOwHUF/kcmGqdPkzW2Sd6irD 6+G4SPo3rez8pn5UhjmzAfYKRkdnkcBl/vdquNKFzB0jE28MkviYPv1BwrrNU6FjA4PfC1BgOKB kmWEMJtAhCcZUzd1wc+wWLif03GZvtcnVXNdKBcIhcZlzcffH0t1HnRDyx8EnYASL+c X-Google-Smtp-Source: AGHT+IEvX8sJF+22nN0j17naG8VSCjm7ShZTKBpfpfH1JpRjytMJdmQiTcsKEjTDhwAIeG3CgHjK7A== X-Received: by 2002:a05:6000:156c:b0:386:1cd3:8a0e with SMTP id ffacd0b85a97d-38a8731007fmr3232471f8f.48.1736355930091; Wed, 08 Jan 2025 09:05:30 -0800 (PST) Received: from phenom.ffwll.local ([2a02:168:57f4:0:5485:d4b2:c087:b497]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38a1c89e357sm54692891f8f.72.2025.01.08.09.05.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Jan 2025 09:05:29 -0800 (PST) Date: Wed, 8 Jan 2025 18:05:27 +0100 From: Simona Vetter To: "Huang, Honglei1" Cc: Demi Marie Obenour , 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 Subject: Re: [RFC PATCH 3/3] drm/virtio: implement blob userptr resource object Message-ID: Mail-Followup-To: "Huang, Honglei1" , Demi Marie Obenour , 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 References: <20241220100409.4007346-1-honglei1.huang@amd.com> <20241220100409.4007346-3-honglei1.huang@amd.com> <2fb36b50-4de2-4060-a4b7-54d221db8647@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Operating-System: Linux phenom 6.12.3-amd64 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" 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. The other option is that hsakmt/kfd api is completely busted, and that's kinda not a kernel problem. -Sima -- Simona Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch