linux-kernel - Re: [report] DMA-API: platform vgem: mapping sg segment longer than device claims to support [len=1048576] [max=65536]

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Message-ID: <1506c0e7-85a3-47e4-9c70-77b01e30accb@linux.dev>
Date: Fri, 20 Jun 2025 00:07:04 +0800
From: Zenghui Yu <zenghui.yu@...ux.dev>
To: Thomas Zimmermann <tzimmermann@...e.de>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 airlied@...il.com, simona@...ll.ch, maarten.lankhorst@...ux.intel.com,
 mripard@...nel.org
Subject: Re: [report] DMA-API: platform vgem: mapping sg segment longer than
 device claims to support [len=1048576] [max=65536]

Hi Thomas,

On 2025/6/19 00:25, Thomas Zimmermann wrote:
> Hi
> 
> Am 18.06.25 um 18:03 schrieb Zenghui Yu:
> > Hi all,
> >
> > Running the dmabuf-heap test [*] on mainline kernel triggers the
> > following splat:
> >
> >  ------------[ cut here ]------------
> >  DMA-API: platform vgem: mapping sg segment longer than device claims to support [len=1048576] [max=65536]
> 
> Thanks for the bug report. We have a possible fix in the latest drm-
> misc-next tree. Does it work if use replace DRM_GEM_SHMEM_DRIVER_OPS
> with DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT at [1]?
> 
> [1] https://elixir.bootlin.com/linux/v6.16-rc2/source/drivers/gpu/drm/vgem/vgem_drv.c#L118

Thanks for the heads up! So I applied commit 660cd44659a0
("drm/shmem-helper: Import dmabuf without mapping its sg_table") [*] in
my local tree, together with your suggestion:

diff --git a/drivers/gpu/drm/vgem/vgem_drv.c
b/drivers/gpu/drm/vgem/vgem_drv.c
index 2752ab4f1c97..ba0d4e611bd2 100644
--- a/drivers/gpu/drm/vgem/vgem_drv.c
+++ b/drivers/gpu/drm/vgem/vgem_drv.c
@@ -115,7 +115,7 @@ static const struct drm_driver vgem_driver = {
 	.num_ioctls 			= ARRAY_SIZE(vgem_ioctls),
 	.fops				= &vgem_driver_fops,

-	DRM_GEM_SHMEM_DRIVER_OPS,
+	DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT,
 	.gem_create_object		= vgem_gem_create_object,

 	.name	= DRIVER_NAME,

The warning message disappeared with that. Thanks again!

[*]
https://gitlab.freedesktop.org/drm/kernel/-/commit/660cd44659a05c5fbfce6d2bb1ce448aa0f35594

Zenghui