Commit a6829c35 authored Feb 02, 2021 by Colin Xu Committed by Michael S. Tsirkin Feb 23, 2021

virtio_input: Prevent EV_MSC/MSC_TIMESTAMP loop storm for MT.



In 'commit 29cc309d ("HID: hid-multitouch: forward MSC_TIMESTAMP")',
EV_MSC/MSC_TIMESTAMP is added to each before EV_SYN event. EV_MSC is
configured as INPUT_PASS_TO_ALL.
In case of a touch device which report MSC_TIMESTAMP:
  BE pass EV_MSC/MSC_TIMESTAMP to FE on receiving event from evdev.
  FE pass EV_MSC/MSC_TIMESTAMP back to BE.
  BE writes EV_MSC/MSC_TIMESTAMP to evdev due to INPUT_PASS_TO_ALL.
  BE receives extra EV_MSC/MSC_TIMESTAMP and pass to FE.
>>> Each new frame becomes larger and larger.

Disable EV_MSC/MSC_TIMESTAMP forwarding for MT.

V2: Rebase.

Signed-off-by: Colin Xu <colin.xu@intel.com>
Link: https://lore.kernel.org/r/20210202001923.6227-1-colin.xu@intel.com


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>

parent d1e9aa9c

drivers/virtio/virtio_input.c

+15 −0

Original line number	Diff line number	Diff line
		@@ -64,6 +64,21 @@ static int virtinput_send_status(struct virtio_input *vi,
		unsigned long flags;
		int rc;

		/*
		* Since 29cc309d8bf1 (HID: hid-multitouch: forward MSC_TIMESTAMP),
		* EV_MSC/MSC_TIMESTAMP is added to each before EV_SYN event.
		* EV_MSC is configured as INPUT_PASS_TO_ALL.
		* In case of touch device:
		* BE pass EV_MSC/MSC_TIMESTAMP to FE on receiving event from evdev.
		* FE pass EV_MSC/MSC_TIMESTAMP back to BE.
		* BE writes EV_MSC/MSC_TIMESTAMP to evdev due to INPUT_PASS_TO_ALL.
		* BE receives extra EV_MSC/MSC_TIMESTAMP and pass to FE.
		* >>> Each new frame becomes larger and larger.
		* Disable EV_MSC/MSC_TIMESTAMP forwarding for MT.
		*/
		if (vi->idev->mt && type == EV_MSC && code == MSC_TIMESTAMP)
		return 0;

		stsbuf = kzalloc(sizeof(*stsbuf), GFP_ATOMIC);
		if (!stsbuf)
		return -ENOMEM;