linux-kernel - Re: [PATCH] gpu: Move DRM buddy allocator one level up

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Message-ID: <CAPM=9tyN_A3oEyQZCOWaLO1orO6oKX0ZukJHR7cFy12Go+7d=A@mail.gmail.com>
Date: Tue, 25 Nov 2025 19:08:37 +1000
From: Dave Airlie <airlied@...il.com>
To: Christian König <christian.koenig@....com>
Cc: John Hubbard <jhubbard@...dia.com>, Joel Fernandes <joelagnelf@...dia.com>, 
	linux-kernel@...r.kernel.org, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, Simona Vetter <simona@...ll.ch>, Jonathan Corbet <corbet@....net>, 
	Alex Deucher <alexander.deucher@....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 Hellström <thomas.hellstrom@...ux.intel.com>, 
	Helge Deller <deller@....de>, Danilo Krummrich <dakr@...nel.org>, 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>, 
	Björn 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>, 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] gpu: Move DRM buddy allocator one level up

On Tue, 25 Nov 2025 at 18:11, Christian König <christian.koenig@....com> wrote:
>
> On 11/25/25 08:59, John Hubbard wrote:
> > On 11/24/25 11:54 PM, Christian König wrote:
> >> On 11/25/25 08:49, Dave Airlie wrote:
> >>> On Tue, 25 Nov 2025 at 17:45, Christian König <christian.koenig@....com> wrote:
> > ...
> >> My question is why exactly is nova separated into nova-core and nova-drm? That doesn't seem to be necessary in the first place.
> >>
> > The idea is that nova-core allows building up a separate software stack for
> > VFIO, without pulling in any DRM-specific code that a hypervisor (for example)
> > wouldn't need. That makes for a smaller, more security-auditable set of code
> > for that case.
>
> Well that is the same argument used by some AMD team to maintain a separate out of tree hypervisor for nearly a decade.
>
> Additional to that the same argument has also been used to justify the KFD node as alternative API to DRM for compute.
>
> Both cases have proven to be extremely bad ideas.
>
> Background is that except for all the legacy stuff the DRM API is actually very well thought through and it is actually quite hard to come up with something similarly well.
>

Well you just answered your own question, why is AMD maintaining GIM
instead of solving this upstream with a split model? the nova-core/drm
split would be perfect for GIM.

kfd was a terrible idea, and we don't intend to offer userspace
multiple APIs with nova, nova-drm will be the primary userspace API
provider. nova-core will not provide userspace API, it will provide an
API to nova-drm and an API to the vgpu driver which will provide it's
own userspace API without graphics or compute, just enough to setup
VFs.

Dave.