linux-kernel - Re: [PATCH v9 14/42] drm/msm: Convert vm locking

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Message-ID: <b0a36f3d-706a-4622-89a1-f88c6255e4fb@dakr.org>
Date: Tue, 12 Aug 2025 10:58:42 +0200
From: Danilo Krummrich <kernel@...r.org>
To: Rob Clark <robin.clark@....qualcomm.com>
Cc: dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
 freedreno@...ts.freedesktop.org, Connor Abbott <cwabbott0@...il.com>,
 Antonino Maniscalco <antomani103@...il.com>,
 Danilo Krummrich <dakr@...hat.com>, Rob Clark <robdclark@...omium.org>,
 Dmitry Baryshkov <lumag@...nel.org>, Abhinav Kumar
 <abhinav.kumar@...ux.dev>, Jessica Zhang <jessica.zhang@....qualcomm.com>,
 Sean Paul <sean@...rly.run>, Marijn Suijten <marijn.suijten@...ainline.org>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Sumit Semwal <sumit.semwal@...aro.org>,
 Christian König <christian.koenig@....com>,
 open list <linux-kernel@...r.kernel.org>,
 "open list:DMA BUFFER SHARING FRAMEWORK:Keyword:bdma_(?:buf|fence|resv)b"
 <linux-media@...r.kernel.org>,
 "moderated list:DMA BUFFER SHARING FRAMEWORK:Keyword:bdma_(?:buf|fence|resv)b"
 <linaro-mm-sig@...ts.linaro.org>
Subject: Re: [PATCH v9 14/42] drm/msm: Convert vm locking

On 6/29/25 10:12 PM, Rob Clark wrote:
> +	/*
> +	 * We mostly want to use DRM_GPUVM_RESV_PROTECTED, except that
> +	 * makes drm_gpuvm_bo_evict() a no-op for extobjs (ie. we loose
> +	 * tracking that an extobj is evicted) :facepalm:
> +	 */

Yeah, it's a consequence of this locking scheme and I really hate it. However,
you don't entirely loose tracking:

The next time you call drm_gpuvm_prepare_objects() it will be added to the list
[1] and hence picked up by subsequent validation through drm_gpuvm_validate().

[1] https://elixir.bootlin.com/linux/v6.16/source/drivers/gpu/drm/drm_gpuvm.c#L1154