2021-02-02 00:21:33

by Colin Xu

Subject: [PATCH V2] virtio_input: Prevent EV_MSC/MSC_TIMESTAMP loop storm for MT.

In 'commit 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 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 <[email protected]>
---
drivers/virtio/virtio_input.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)

diff --git a/drivers/virtio/virtio_input.c b/drivers/virtio/virtio_input.c
index f1f6208edcf5..244965c20d9b 100644
--- a/drivers/virtio/virtio_input.c
+++ b/drivers/virtio/virtio_input.c
@@ -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;
--
2.30.0

2021-02-03 14:30:34

by Gerd Hoffmann

Subject: Re: [PATCH V2] virtio_input: Prevent EV_MSC/MSC_TIMESTAMP loop storm for MT.

Hi,

> + /*
> + * 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;
> +

Reviewed-by: Gerd Hoffmann <[email protected]>

take care,
Gerd