Re: [PATCH 1/2] drm/msm: Avoid div-by-zero in dpu_crtc_atomic_check()

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On 2020-09-02 03:29, Stephen Boyd wrote:
The cstate->num_mixers member is only set to a non-zero value once
dpu_encoder_virt_mode_set() is called, but the atomic check function can be called by userspace before that. Let's avoid the div-by-zero here and
inside _dpu_crtc_setup_lm_bounds() by skipping this part of the atomic
check if dpu_encoder_virt_mode_set() hasn't been called yet. This fixes
an UBSAN warning:

UBSAN: Undefined behaviour in drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c:860:31
 division by zero
 CPU: 7 PID: 409 Comm: frecon Tainted: G S                5.4.31 #128
 Hardware name: Google Trogdor (rev0) (DT)
 Call trace:
  dump_backtrace+0x0/0x14c
  show_stack+0x20/0x2c
  dump_stack+0xa0/0xd8
  __ubsan_handle_divrem_overflow+0xec/0x110
  dpu_crtc_atomic_check+0x97c/0x9d4
  drm_atomic_helper_check_planes+0x160/0x1c8
  drm_atomic_helper_check+0x54/0xbc
  drm_atomic_check_only+0x6a8/0x880
  drm_atomic_commit+0x20/0x5c
  drm_atomic_helper_set_config+0x98/0xa0
  drm_mode_setcrtc+0x308/0x5dc
  drm_ioctl_kernel+0x9c/0x114
  drm_ioctl+0x2ac/0x4b0
  drm_compat_ioctl+0xe8/0x13c
  __arm64_compat_sys_ioctl+0x184/0x324
  el0_svc_common+0xa4/0x154
  el0_svc_compat_handler+0x

Cc: Abhinav Kumar <abhinavk@xxxxxxxxxxxxxx>
Cc: Jeykumar Sankaran <jsanka@xxxxxxxxxxxxxx>
Cc: Jordan Crouse <jcrouse@xxxxxxxxxxxxxx>
Cc: Sean Paul <seanpaul@xxxxxxxxxxxx>
Fixes: 25fdd5933e4c ("drm/msm: Add SDM845 DPU support")
Signed-off-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>
---

Tested-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>

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