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Thu, 29 Jan 2026 01:49:23 +0000 Received: from DS0PR12MB6486.namprd12.prod.outlook.com ([fe80::88a9:f314:c95f:8b33]) by DS0PR12MB6486.namprd12.prod.outlook.com ([fe80::88a9:f314:c95f:8b33%4]) with mapi id 15.20.9542.010; Thu, 29 Jan 2026 01:49:23 +0000 Message-ID: <051a0b2d-7fcc-4c6a-94b1-8d67334fbe3c@nvidia.com> Date: Wed, 28 Jan 2026 20:49:16 -0500 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC v6 05/26] nova-core: mm: Add support to use PRAMIN windows to write to VRAM To: John Hubbard , Danilo Krummrich Cc: Zhi Wang , linux-kernel@vger.kernel.org, Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Jonathan Corbet , Alex Deucher , Christian Koenig , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , Huang Rui , Matthew Auld , Matthew Brost , Lucas De Marchi , Thomas Hellstrom , Helge Deller , Alice Ryhl , Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , Bjorn Roy Baron , Benno Lossin , Andreas Hindborg , Trevor Gross , Alistair Popple , Timur Tabi , Edwin Peer , Alexandre Courbot , Andrea Righi , Andy Ritger , Alexey Ivanov , Balbir Singh , Philipp Stanner , Elle Rhumsaa , Daniel Almeida , nouveau@lists.freedesktop.org, dri-devel@lists.freedesktop.org, rust-for-linux@vger.kernel.org, linux-doc@vger.kernel.org, amd-gfx@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, intel-xe@lists.freedesktop.org, linux-fbdev@vger.kernel.org References: <20260120204303.3229303-1-joelagnelf@nvidia.com> <20260120204303.3229303-6-joelagnelf@nvidia.com> <20260121100745.2b5a58e5.zhiw@nvidia.com> Content-Language: en-US From: Joel Fernandes In-Reply-To: Content-Type: text/plain; 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I believe we >>> can avoid non-atomic locks completely - actually I just wrote a patch >>> before I read this email to do just. If we are to forbid any locking at >>> all, that might require some careful redesign to handle the above race >>> afaics. >> >> It's not about the locks themselves, sleeping locks are fine too. It's about >> holding locks that are held elsewhere when doing memory allocations that can >> call back into MMU notifiers or the shrinker. > > If you look at core kernel mm, you'll find a similar constraint: avoid > holding any locks while allocating--unless you are in the reclaim code > itself. > > Especially when dealing with page tables. > > So this is looking familiar to me and I agree with the constraint, fwiw. Right, so similar to core kernel mm, we need to separate PT allocation from the lock needed for PT writing. Essentially never allocating PT pages in the dma-fence critical paths. We already have separate locks for both these (buddy versus vmm), so it should be doable with some adjustments. I will study the dma-fence further and revise patches. Thanks. -- Joel Fernandes