linux-kernel - Re: [PATCH v2 4/9] drm/msm/A6xx: Implement preemption for A7XX targets

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Message-ID: <CAF6AEGtxCnoyrEHPknV7C9XO3OcTpSOmGq-j2K7UDKXF1j0ssA@mail.gmail.com>
Date: Fri, 30 Aug 2024 11:01:23 -0700
From: Rob Clark <robdclark@...il.com>
To: Antonino Maniscalco <antomani103@...il.com>
Cc: Sean Paul <sean@...rly.run>, Konrad Dybcio <konrad.dybcio@...aro.org>, 
	Abhinav Kumar <quic_abhinavk@...cinc.com>, Dmitry Baryshkov <dmitry.baryshkov@...aro.org>, 
	Marijn Suijten <marijn.suijten@...ainline.org>, David Airlie <airlied@...il.com>, 
	Daniel Vetter <daniel@...ll.ch>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, linux-arm-msm@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org, 
	linux-kernel@...r.kernel.org, Sharat Masetty <smasetty@...eaurora.org>, 
	Neil Armstrong <neil.armstrong@...aro.org>
Subject: Re: [PATCH v2 4/9] drm/msm/A6xx: Implement preemption for A7XX targets

On Fri, Aug 30, 2024 at 8:33 AM Antonino Maniscalco
<antomani103@...il.com> wrote:
>
> This patch implements preemption feature for A6xx targets, this allows
> the GPU to switch to a higher priority ringbuffer if one is ready. A6XX
> hardware as such supports multiple levels of preemption granularities,
> ranging from coarse grained(ringbuffer level) to a more fine grained
> such as draw-call level or a bin boundary level preemption. This patch
> enables the basic preemption level, with more fine grained preemption
> support to follow.
>
> Signed-off-by: Sharat Masetty <smasetty@...eaurora.org>
> Signed-off-by: Antonino Maniscalco <antomani103@...il.com>
> Tested-by: Neil Armstrong <neil.armstrong@...aro.org> # on SM8650-QRD
> ---
>  drivers/gpu/drm/msm/Makefile              |   1 +
>  drivers/gpu/drm/msm/adreno/a6xx_gpu.c     | 323 +++++++++++++++++++++-
>  drivers/gpu/drm/msm/adreno/a6xx_gpu.h     | 168 ++++++++++++
>  drivers/gpu/drm/msm/adreno/a6xx_preempt.c | 431 ++++++++++++++++++++++++++++++
>  drivers/gpu/drm/msm/msm_ringbuffer.h      |   7 +
>  5 files changed, 921 insertions(+), 9 deletions(-)
>

[snip]

> +
> +int a6xx_preempt_submitqueue_setup(struct msm_gpu *gpu,
> +               struct msm_gpu_submitqueue *queue)
> +{
> +       void *ptr;
> +
> +       /*
> +        * Create a per submitqueue buffer for the CP to save and restore user
> +        * specific information such as the VPC streamout data.
> +        */
> +       ptr = msm_gem_kernel_new(gpu->dev, A6XX_PREEMPT_USER_RECORD_SIZE,
> +                       MSM_BO_WC, gpu->aspace, &queue->bo, &queue->bo_iova);

Can this be MSM_BO_MAP_PRIV?  Otherwise it is visible (and writeable)
by other proceess's userspace generated cmdstream.

And a similar question for the scratch_bo..  I'd have to give some
thought to what sort of mischief could be had, but generall kernel
mappings that are not MAP_PRIV are a thing to be careful about.

BR,
-R