[PATCH] media: videobuf2: Set vma_flags in vb2_dma_sg_mmap

[Janne Grunau <j@jannau.net>]

vb2_dma_contig sets VMA flags VM_DONTEXPAND and VM_DONTDUMP and I do not
see a reason why vb2_dma_sg should behave differently. This avoids
hitting `WARN_ON(!(vma->vm_flags & VM_DONTEXPAND));` in
drm_gem_mmap_obj() during mmap() of an imported dma-buf from the out of
tree Apple ISP camera capture driver which uses vb2_dma_sg_memops.

gst-launch-1.0 v4l2src ! gtk4paintablesink

[   38.201528] ------------[ cut here ]------------
[   38.202135] WARNING: CPU: 7 PID: 2362 at drivers/gpu/drm/drm_gem.c:1144 drm_gem_mmap_obj+0x1f8/0x210
[   38.203278] Modules linked in: rfcomm snd_seq_dummy snd_hrtimer
snd_seq snd_seq_device uinput nf_conntrack_netbios_ns
nf_conntrack_broadcast nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib
nft_reject_inet nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat
nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nf_tables qrtr bnep
nls_ascii i2c_dev loop fuse dm_multipath nfnetlink brcmfmac_wcc
hid_magicmouse hci_bcm4377 brcmfmac brcmutil bluetooth ecdh_generic
cfg80211 ecc btrfs xor xor_neon rfkill hid_apple raid6_pq joydev
aop_als apple_nvmem_spmi industrialio snd_soc_aop apple_z2
snd_soc_cs42l84 tps6598x snd_soc_tas2764 macsmc_reboot spi_nor
macsmc_hwmon rtc_macsmc gpio_macsmc macsmc_power regmap_spmi
macsmc_input dockchannel_hid panel_summit appledrm nvme_apple dwc3
snd_soc_macaudio drm_client_lib nvme_core phy_apple_atc hwmon
apple_sart apple_dockchannel macsmc apple_rtkit_helper
spmi_apple_controller aop apple_wdt mfd_core nvmem_apple_efuses
pinctrl_apple_gpio apple_isp apple_dcp videobuf2_dma_sg mux_core
spi_apple
[   38.203300]  videobuf2_memops i2c_pasemi_platform snd_soc_apple_mca videobuf2_v4l2 videodev clk_apple_nco videobuf2_common snd_pcm_dmaengine adpdrm asahi apple_admac adpdrm_mipi drm_dma_helper pwm_apple i2c_pasemi_core drm_display_helper mc cec apple_dart ofpart apple_soc_cpufreq leds_pwm phram
[   38.217677] CPU: 7 UID: 1000 PID: 2362 Comm: gst-launch-1.0 Tainted: G        W           6.17.6+ #asahi-dev PREEMPT(full)
[   38.219040] Tainted: [W]=WARN
[   38.219398] Hardware name: Apple MacBook Pro (13-inch, M2, 2022) (DT)
[   38.220213] pstate: 21400005 (nzCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
[   38.221088] pc : drm_gem_mmap_obj+0x1f8/0x210
[   38.221643] lr : drm_gem_mmap_obj+0x78/0x210
[   38.222178] sp : ffffc0008dc678e0
[   38.222579] x29: ffffc0008dc678e0 x28: 0000000000042a97 x27: ffff8000b701b480
[   38.223465] x26: 00000000000000fb x25: ffffc0008dc67d20 x24: ffffc0008dc67968
[   38.224402] x23: ffff8000e3ca5600 x22: ffff8000265b7800 x21: ffff80003000c0c0
[   38.225279] x20: 0000000000000000 x19: ffff8000b68c5200 x18: ffffc0008dc67968
[   38.226151] x17: 0000000000000000 x16: 0000000000000000 x15: ffffc000810a30a8
[   38.227042] x14: 00007fff637effff x13: 00005555de91ffff x12: 00007fff63293fff
[   38.227942] x11: 0000000000000000 x10: ffff8000184ecf08 x9 : ffffc0007a1900c8
[   38.228824] x8 : ffffc0008dc67968 x7 : 0000000000000012 x6 : ffffc0015cf1c000
[   38.229703] x5 : ffffc0008dc676a0 x4 : ffffc00081a27dc0 x3 : 0000000000000038
[   38.230607] x2 : 0000000000000003 x1 : 0000000000000003 x0 : 00000000100000fb
[   38.231488] Call trace:
[   38.231806]  drm_gem_mmap_obj+0x1f8/0x210 (P)
[   38.232342]  drm_gem_mmap+0x140/0x260
[   38.232813]  __mmap_region+0x488/0x9a0
[   38.233277]  mmap_region+0xd0/0x148
[   38.233703]  do_mmap+0x350/0x5c0
[   38.234148]  vm_mmap_pgoff+0x14c/0x200
[   38.234612]  ksys_mmap_pgoff+0x150/0x208
[   38.235107]  __arm64_sys_mmap+0x34/0x50
[   38.235611]  invoke_syscall+0x50/0x120
[   38.236075]  el0_svc_common.constprop.0+0x48/0xf0
[   38.236680]  do_el0_svc+0x24/0x38
[   38.237113]  el0_svc+0x38/0x168
[   38.237507]  el0t_64_sync_handler+0xa0/0xe8
[   38.238034]  el0t_64_sync+0x198/0x1a0
[   38.238491] ---[ end trace 0000000000000000 ]---

There were discussions in [1] at the end of 2023 that mmap() on imported
dma-bufs should not be supported but as of v6.17 drm_gem_shmem_mmap() in
drm_gem_shmem_helper.c still supports it.
This might affect all gpu or accel drivers using drm_gem_shmem_mmap() or
the wrapper drm_gem_shmem_object_mmap().

[1] https://lore.kernel.org/dri-devel/bc7f7844-0aa3-4802-b203-69d58e8be2fa@linux.intel.com/

Cc: stable@vger.kernel.org
Fixes: 5ba3f757f059 ("[media] v4l: videobuf2: add DMA scatter/gather allocator")
Signed-off-by: Janne Grunau <j@jannau.net>
---
included DRM maintainers due to warning triggered from DRM code.
---
 drivers/media/common/videobuf2/videobuf2-dma-sg.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/media/common/videobuf2/videobuf2-dma-sg.c b/drivers/media/common/videobuf2/videobuf2-dma-sg.c
index b3bf2173c14e1b3bedb8ab0bd60c889a0b97cbe3..7c30731cb9a57bebb3cf418e627e7c9f09ba8642 100644
--- a/drivers/media/common/videobuf2/videobuf2-dma-sg.c
+++ b/drivers/media/common/videobuf2/videobuf2-dma-sg.c
@@ -345,6 +345,7 @@ static int vb2_dma_sg_mmap(void *buf_priv, struct vm_area_struct *vma)
 		return err;
 	}
 
+	vm_flags_set(vma, VM_DONTEXPAND | VM_DONTDUMP);
 	/*
 	 * Use common vm_area operations to track buffer refcount.
 	 */

---
base-commit: 05f7e89ab9731565d8a62e3b5d1ec206485eeb0b
change-id: 20260215-media-vb2-dma-sg-0fa33fdafdde

Best regards,
-- 
Janne Grunau <j@jannau.net>