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

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Message-ID: <CACSVV02+hE1j9vN_BU5pwz_4cnJjj==j-L5oPeFWCvEr+1HiFQ@mail.gmail.com>
Date: Tue, 12 Aug 2025 18:52:00 -0700
From: Rob Clark <rob.clark@....qualcomm.com>
To: Danilo Krummrich <kernel@...r.org>
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 Tue, Aug 12, 2025 at 1:58 AM Danilo Krummrich <kernel@...r.org> wrote:
>
> 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

Hmm, maybe the issue was with legacy (non-vm_bind) contexts, which use
drm_exec directly for locking?  I guess I can try to revisit that..

BR,
-R