drm/amdgpu: gate VM CPU HDP flush on reset lock

drm/amdgpu: gate VM CPU HDP flush on reset lock

During GPU reset, the application could still run CPU page table updates. Each commit called
amdgpu_device_flush_hdp(), which on SR-IOV sends work through the KIQ ring.
That can advance sync_seq while the GPU is being reset,
leaving fence writeback out of sync and causing amdgpu_fence_emit_polling()
to time out on later KIQ use.

Fix:
amdgpu_vm_cpu_commit():
  Reset will flush HDP anyway, the HDP flush in amdgpu_vm_cpu_commit() can be skipped
  when a reset is ongoging.
  Take reset_domain->sem with down_read_trylock() before amdgpu_device_flush_hdp().
  If the reset path holds the write lock, skip the HDP flush so no HDP-related HW
  access (including KIQ) runs during reset; state is re-established after reset.

Signed-off-by: Chenglei Xie <Chenglei.Xie@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org