linux-kernel - Re: [PATCH RFC v6 05/26] nova-core: mm: Add support to use PRAMIN windows to write to VRAM

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Message-ID: <97af2d85-a905-44d4-951f-e56a40f4312e@nvidia.com>
Date: Thu, 29 Jan 2026 17:11:49 -0800
From: John Hubbard <jhubbard@...dia.com>
To: Joel Fernandes <joelagnelf@...dia.com>, Danilo Krummrich <dakr@...nel.org>
Cc: Zhi Wang <zhiw@...dia.com>, linux-kernel@...r.kernel.org,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Jonathan Corbet <corbet@....net>, Alex Deucher <alexander.deucher@....com>,
 Christian Koenig <christian.koenig@....com>,
 Jani Nikula <jani.nikula@...ux.intel.com>,
 Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
 Rodrigo Vivi <rodrigo.vivi@...el.com>, Tvrtko Ursulin
 <tursulin@...ulin.net>, Huang Rui <ray.huang@....com>,
 Matthew Auld <matthew.auld@...el.com>,
 Matthew Brost <matthew.brost@...el.com>,
 Lucas De Marchi <lucas.demarchi@...el.com>,
 Thomas Hellstrom <thomas.hellstrom@...ux.intel.com>,
 Helge Deller <deller@....de>, Alice Ryhl <aliceryhl@...gle.com>,
 Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
 Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
 Bjorn Roy Baron <bjorn3_gh@...tonmail.com>, Benno Lossin
 <lossin@...nel.org>, Andreas Hindborg <a.hindborg@...nel.org>,
 Trevor Gross <tmgross@...ch.edu>, Alistair Popple <apopple@...dia.com>,
 Timur Tabi <ttabi@...dia.com>, Edwin Peer <epeer@...dia.com>,
 Alexandre Courbot <acourbot@...dia.com>, Andrea Righi <arighi@...dia.com>,
 Andy Ritger <aritger@...dia.com>, Alexey Ivanov <alexeyi@...dia.com>,
 Balbir Singh <balbirs@...dia.com>, Philipp Stanner <phasta@...nel.org>,
 Elle Rhumsaa <elle@...thered-steel.dev>,
 Daniel Almeida <daniel.almeida@...labora.com>,
 nouveau@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
 rust-for-linux@...r.kernel.org, linux-doc@...r.kernel.org,
 amd-gfx@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
 intel-xe@...ts.freedesktop.org, linux-fbdev@...r.kernel.org
Subject: Re: [PATCH RFC v6 05/26] nova-core: mm: Add support to use PRAMIN
 windows to write to VRAM

On 1/29/26 4:26 PM, Joel Fernandes wrote:
> Hi, Danilo, all,
> 
> Based on the below discussion and research, I came up with some deadlock
> scenarios that we need to handle in the v6 series of these patches. Please let
> me know if I missed something below. At the moment, off the top I identified
> that we are doing GFP_KERNEL memory allocations inside GPU buddy allocator
> during map/unmap. I will work on solutions for that. Thanks.
> 
> All deadlock scenarios
> ----------------------
> The gist is, in the DMA fence signaling critical path we cannot acquire
> resources (locks or memory allocation etc) that are already acquired when a
> fence is being waited on to be signaled. So we have to careful which resources
> we acquire, and also we need to be careful which paths in the driver we do any
> memory allocations under locks that we need in the dma-fence signaling critical
> path (when doing the virtual memory map/unmap)

unmap? Are you seeing any allocations happening during unmap? I don't
immediately see any, but that sounds surprising.

thanks,
-- 
John Hubbard