linux-kernel - Re: [PATCH v2 1/3] drm_gem: add mutex to drm_gem

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Message-ID: <20250822130933.50bf1746@fedora>
Date: Fri, 22 Aug 2025 13:09:33 +0200
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: 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>, Danilo Krummrich
 <dakr@...nel.org>, Daniel Almeida <daniel.almeida@...labora.com>, Steven
 Price <steven.price@....com>, Liviu Dudau <liviu.dudau@....com>, Rob Clark
 <robin.clark@....qualcomm.com>, Rob Herring <robh@...nel.org>, Miguel Ojeda
 <ojeda@...nel.org>, Boqun Feng <boqun.feng@...il.com>, Gary Guo
 <gary@...yguo.net>, "Björn Roy Baron"
 <bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>, Andreas
 Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v2 1/3] drm_gem: add mutex to drm_gem_object.gpuva

On Fri, 22 Aug 2025 10:57:26 +0000
Alice Ryhl <aliceryhl@...gle.com> wrote:

> On Fri, Aug 22, 2025 at 11:52:21AM +0200, Boris Brezillon wrote:
> > On Fri, 22 Aug 2025 09:28:24 +0000
> > 
> > Maybe it's time we start moving some bits of the gpuva field docs next
> > to the fields they describe:
> > 
> > 	/**
> > 	 * @gpuva: Fields used by GPUVM to manage mappings pointing to this GEM object.
> > 	 */
> > 	struct {
> > 		/**
> > 		 * @gpuva.list: list of GPU VAs attached to this GEM object.
> > 		 *
> > 		 * Drivers should lock list accesses with the GEMs &dma_resv lock
> > 		 * (&drm_gem_object.resv) or &drm_gem_object.gpuva.lock if the
> > 		 * list is being updated in places where the resv lock can't be
> > 		 * acquired (fence signalling path).
> > 		 */
> > 		struct list_head list;  
> 
> This isn't a new issue, but it's somewhat confusing to call it a list of
> VAs when it's a list of vm_bos.

Yep, that's true.

> 
> > 		/**
> > 		 * @gpuva.lock: lock protecting access to &drm_gem_object.gpuva.list
> > 		 * when the resv lock can't be used.
> > 		 *
> > 		 * Should only be used when the VM is being modified in a fence
> > 		 * signalling path, otherwise you should use &drm_gem_object.resv to
> > 		 * protect accesses to &drm_gem_object.gpuva.list.
> > 		 */
> > 		struct mutex lock;
> > 
> > 		...
> > 	};
> >   
> 
> Alice