linux-kernel - Re: [PATCH 1/2] drm/gpuvm: add deferred vm

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Message-ID: <7aa3f464-a3d0-47a0-b044-d8db93f45918@kernel.org>
Date: Mon, 8 Sep 2025 14:20:35 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Boris Brezillon <boris.brezillon@...labora.com>
Cc: Alice Ryhl <aliceryhl@...gle.com>, Matthew Brost
 <matthew.brost@...el.com>,
 Thomas Hellström <thomas.hellstrom@...ux.intel.com>,
 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>,
 Steven Price <steven.price@....com>,
 Daniel Almeida <daniel.almeida@...labora.com>,
 Liviu Dudau <liviu.dudau@....com>, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH 1/2] drm/gpuvm: add deferred vm_bo cleanup

On 9/8/25 2:11 PM, Boris Brezillon wrote:
> On Mon, 08 Sep 2025 13:11:32 +0200
> "Danilo Krummrich" <dakr@...nel.org> wrote:
>> I'm saying exactly what you say: "has to be a special unlink function" ->
>> drm_gpuva_unlink_defer_put(). :)
> 
> I don't see how calling drm_gpuva_unlink() instead of
> drm_gpuva_unlink_defer_put() would leak the vm_bo though.

Initially (i.e. a few mails back), it sounded to me as if you'd propose to drop
the drm_gpuva's vm_bo reference only when it is freed.

>> No, drivers can't iterate the evict/extobj lists directly; or at least this is
>> not intended by GPUVM's API and if drivers do so, this is considered peeking
>> into GPUVM internals, so drivers are on their own anyways.
>>
>> Iterators, such as for_each_vm_bo_in_list() are not exposed to drivers.
> 
> Okay, that's a good thing. I thought Xe was doing some funky stuff with
> the list...

Maybe, I don't know. If they do so, the should send patches adding the
corresponding iterators and provide a rationale why drivers need to access those
lists directly and why we can't provide an API that handles the overall
use-case, such as drm_gpuvm_prepare_objects(), etc.