When rtl8139 card is running in standard mode, it is very easy
to overlflow and the receive buffer and get into a siutation
where all packets are dropped. Simply reproduction case is
to ping the guest from the host with 6500 byte packets.
There are actually 2 problems here.
1) When the rtl8129 buffer is overflow, the card emulation
returns the size of the packet back to queue transmission.
This signals successful reception even though the packet
has been dropped. The proper solution is to return 0, so
that the packet is re-queued and will be resubmitted later.
2) When packets are sized such that the fragments end up completely
filling the receive buffer without overflow, the device thinks
that the buffer is actually empty (instead of full). This causes
next packet to over-write the existing packets. With the above
ping reproducer, ever ICMP packet fills the buffer and thus keeps
overwriting the previous packet and never waking up the guest.
The solution here is to trap the buffer full condition and let
the guest read the data before writing more data to the rxBuffer.
Vladislav Yasevich (2):
rtl8139: Do not consume the packet during overflow in standard mode.
rtl8139: correctly track full receive buffer in standard mode
hw/net/rtl8139.c | 39 ++++++++++++++++++++++++++++++++++++---
1 file changed, 36 insertions(+), 3 deletions(-)
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1.9.3
