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From: "Kasireddy, Vivek" <vivek.kasireddy@intel.com>
To: Sebastian Ott <sebott@redhat.com>, "dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>, "virtualization@lists.linux.dev"
	<virtualization@lists.linux.dev>, "linux-kernel@vger.kernel.org"
	<linux-kernel@vger.kernel.org>
CC: David Airlie <airlied@redhat.com>, Gerd Hoffmann <kraxel@redhat.com>,
	Daniel Vetter <daniel@ffwll.ch>
Subject: RE: [PATCH RESEND] drm/virtio: set segment size for virtio_gpu device
Thread-Topic: [PATCH RESEND] drm/virtio: set segment size for virtio_gpu
 device
Thread-Index: AQHaTigSom+Pto7E5U++tm9t0IVe9rDpepuA
Date: Wed, 24 Jan 2024 21:24:17 +0000
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> Hej,
>=20
> debug dma code is not happy with virtio gpu (arm64 VM):
>=20
> [  305.881733] ------------[ cut here ]------------
> [  305.883117] DMA-API: virtio-pci 0000:07:00.0: mapping sg segment longe=
r
> than device claims to support [len=3D262144] [max=3D65536]
> [  305.885976] WARNING: CPU: 8 PID: 2002 at kernel/dma/debug.c:1177
> check_sg_segment+0x2d0/0x420
> [  305.888038] Modules linked in: crct10dif_ce(+) polyval_ce polyval_gene=
ric
> ghash_ce virtio_gpu(+) virtio_net net_failover virtio_blk(+) virtio_dma_b=
uf
> virtio_console failover virtio_mmio scsi_dh_r dac scsi_dh_emc scsi_dh_alu=
a
> dm_multipath qemu_fw_cfg
> [  305.893496] CPU: 8 PID: 2002 Comm: (udev-worker) Not tainted 6.7.0 #1
> [  305.895070] Hardware name: QEMU KVM Virtual Machine, BIOS edk2-
> 20230524-3.fc37 05/24/2023
> [  305.897112] pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS
> BTYPE=3D--)
> [  305.897129] pc : check_sg_segment+0x2d0/0x420
> [  305.897139] lr : check_sg_segment+0x2d0/0x420
> [  305.897145] sp : ffff80008ffc69d0
> [  305.897149] x29: ffff80008ffc69d0 x28: dfff800000000000 x27:
> ffffb0232879e578
> [  305.897167] x26: ffffffff00000000 x25: ffffb0232778c060 x24:
> ffff19ee9b2060c0
> [  305.897181] x23: 00000000ffffffff x22: ffffb0232ab9ce10 x21:
> ffff19eece5c64ac
> [  305.906942] x20: 0000000000010000 x19: ffff19eece5c64a0 x18:
> ffff19eec36fc304
> [  305.908633] x17: 6e61687420726567 x16: 6e6f6c20746e656d x15:
> 6765732067732067
> [  305.910352] x14: 00000000f1f1f1f1 x13: 0000000000000001 x12:
> ffff700011ff8cc3
> [  305.912044] x11: 1ffff00011ff8cc2 x10: ffff700011ff8cc2 x9 :
> ffffb02324a70e54
> [  305.913751] x8 : 00008fffee00733e x7 : ffff80008ffc6617 x6 :
> 0000000000000001
> [  305.915451] x5 : ffff80008ffc6610 x4 : 1fffe33e70564622 x3 :
> dfff800000000000
> [  305.917158] x2 : 0000000000000000 x1 : 0000000000000000 x0 :
> ffff19f382b23100
> [  305.918864] Call trace:
> [  305.919474]  check_sg_segment+0x2d0/0x420
> [  305.920443]  debug_dma_map_sg+0x2a0/0x428
> [  305.921402]  __dma_map_sg_attrs+0xf4/0x1a8
> [  305.922388]  dma_map_sgtable+0x7c/0x100
> [  305.923318]  drm_gem_shmem_get_pages_sgt+0x15c/0x328
> [  305.924500]
> virtio_gpu_object_shmem_init.constprop.0.isra.0+0x50/0x628 [virtio_gpu]
> [  305.926390]  virtio_gpu_object_create+0x198/0x478 [virtio_gpu]
> [  305.927802]  virtio_gpu_mode_dumb_create+0x2a0/0x4c8 [virtio_gpu]
> [  305.929272]  drm_mode_create_dumb+0x1c0/0x280
> [  305.930327]  drm_client_framebuffer_create+0x140/0x328
> [  305.931555]  drm_fbdev_generic_helper_fb_probe+0x1bc/0x5c0
> [  305.932871]  __drm_fb_helper_initial_config_and_unlock+0x1e0/0x630
> [  305.934372]  drm_fb_helper_initial_config+0x50/0x68
> [  305.935540]  drm_fbdev_generic_client_hotplug+0x148/0x200
> [  305.936819]  drm_client_register+0x130/0x200
> [  305.937856]  drm_fbdev_generic_setup+0xe8/0x320
> [  305.938932]  virtio_gpu_probe+0x13c/0x2d0 [virtio_gpu]
> [  305.940190]  virtio_dev_probe+0x38c/0x600
> [  305.941153]  really_probe+0x334/0x9c8
> [  305.942047]  __driver_probe_device+0x164/0x3d8
> [  305.943102]  driver_probe_device+0x64/0x180
> [  305.944094]  __driver_attach+0x1d4/0x488
> [  305.945045]  bus_for_each_dev+0x104/0x198
> [  305.946008]  driver_attach+0x44/0x68
> [  305.946892]  bus_add_driver+0x23c/0x4a8
> [  305.947838]  driver_register+0xf8/0x3d0
> [  305.948770]  register_virtio_driver+0x74/0xc8
> [  305.949836]  virtio_gpu_driver_init+0x20/0xff8 [virtio_gpu]
> [  305.951237]  do_one_initcall+0x17c/0x8c0
> [  305.952182]  do_init_module+0x1dc/0x630
> [  305.953106]  load_module+0x10c0/0x1638
> [  305.954012]  init_module_from_file+0xe0/0x140
> [  305.955058]  idempotent_init_module+0x2c0/0x590
> [  305.956174]  __arm64_sys_finit_module+0xb4/0x140
> [  305.957282]  invoke_syscall+0xd8/0x258
> [  305.958187]  el0_svc_common.constprop.0+0x16c/0x240
> [  305.959526]  do_el0_svc+0x48/0x68
> [  305.960456]  el0_svc+0x58/0x118
> [  305.961310]  el0t_64_sync_handler+0x120/0x130
> [  305.962510]  el0t_64_sync+0x194/0x198
> [  305.963509] irq event stamp: 37944
> [  305.964412] hardirqs last  enabled at (37943): [<ffffb02324a7439c>]
> console_unlock+0x1a4/0x1c8
> [  305.966602] hardirqs last disabled at (37944): [<ffffb023276724e4>]
> el1_dbg+0x24/0xa0
> [  305.968535] softirqs last  enabled at (37930): [<ffffb0232475114c>]
> __do_softirq+0x8e4/0xe1c
> [  305.970781] softirqs last disabled at (37925): [<ffffb0232475a9b0>]
> ____do_softirq+0x18/0x30
> [  305.972937] ---[ end trace 0000000000000000 ]---
>=20
> The 64K max_segment size of the device seems to be inherited by PCIs
> default.
> The sg list is crated via this drm helper:
>=20
> struct sg_table *drm_prime_pages_to_sg(struct drm_device *dev,
>   				       struct page **pages, unsigned int
> nr_pages)
> {
> ...
>   	if (dev)
>   		max_segment =3D dma_max_mapping_size(dev->dev);
>   	if (max_segment =3D=3D 0)
>   		max_segment =3D UINT_MAX;
>   	err =3D sg_alloc_table_from_pages_segment(sg, pages, nr_pages, 0,
>   						nr_pages << PAGE_SHIFT,
>   						max_segment, GFP_KERNEL);
> ...
> }
>=20
> I'm a bit puzzled why this uses dma_max_mapping_size() and not
> dma_get_max_seg_size(). But since this is used by a lot of drivers
> I'm not really keen to touch this code that works like this for ages.
>=20
> So let's just make debug dma code aware of the actual segment size
> that's used by the device:
>=20
> --->8
> drm/virtio: set segment size for virtio_gpu device
>=20
> Set the segment size of the virtio_gpu device to the value
> used by the drm helpers when allocating sg lists to fix the
> following complaint from DMA_API debug code:
> DMA-API: virtio-pci 0000:07:00.0: mapping sg segment longer than device
> claims to support [len=3D262144] [max=3D65536]
>=20
> Signed-off-by: Sebastian Ott <sebott@redhat.com>
> ---
>    drivers/gpu/drm/virtio/virtgpu_drv.c | 1 +
>    1 file changed, 1 insertion(+)
>=20
> diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.c
> b/drivers/gpu/drm/virtio/virtgpu_drv.c
> index 4334c7608408..74b2cb3295af 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_drv.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_drv.c
> @@ -94,6 +94,7 @@ static int virtio_gpu_probe(struct virtio_device *vdev)
>    			goto err_free;
>    	}
>=20
> +	dma_set_max_seg_size(dev->dev, dma_max_mapping_size(dev-
> >dev) ? : UINT_MAX);
Acked-by: Vivek Kasireddy <vivek.kasireddy@intel.com>

>    	ret =3D virtio_gpu_init(vdev, dev);
>    	if (ret)
>    		goto err_free;
> --
> 2.43.0
>=20
>=20