hv_utils: drain the timesync packets on onchannelcallback
commit b46b4a8a upstream. There could be instances where a system stall prevents the timesync packets to be consumed. And this might lead to more than one packet pending in the ring buffer. Current code empties one packet per callback and it might be a stale one. So drain all the packets from ring buffer on each callback. Signed-off-by: Vineeth Pillai <viremana@linux.microsoft.com> Reviewed-by: Michael Kelley <mikelley@microsoft.com> Link: https://lore.kernel.org/r/20200821152849.99517-1-viremana@linux.microsoft.com Signed-off-by: Wei Liu <wei.liu@kernel.org> [ The old code in the upstream commit uses HV_HYP_PAGE_SIZE, but the old code in 5.4.y sitll uses PAGE_SIZE. Fixed this manually for 5.4.y. Note: 5.4.y already has the define HV_HYP_PAGE_SIZE, so the new code in in the upstream commit works for 5.4.y. If there are multiple messages in the host-to-guest ringbuffer of the TimeSync device, 5.4.y only handles 1 message, and later the host puts new messages into the ringbuffer without signaling the guest because the ringbuffer is not empty, causing a "hung" ringbuffer. Backported the mainline fix for this issue.] Signed-off-by: Dexuan Cui <decui@microsoft.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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