From b2b012afdd9c03ba8a1619f45301d34f358d367b Mon Sep 17 00:00:00 2001 From: Andrey Smirnov Date: Thu, 11 Jan 2018 13:25:35 +0000 Subject: imx_fec: Change queue flushing heuristics MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit In current implementation, packet queue flushing logic seem to suffer from a deadlock like scenario if a packet is received by the interface before before Rx ring is initialized by Guest's driver. Consider the following sequence of events: 1. A QEMU instance is started against a TAP device on Linux host, running Linux guest, e. g., something to the effect of: qemu-system-arm \ -net nic,model=imx.fec,netdev=lan0 \ netdev tap,id=lan0,ifname=tap0,script=no,downscript=no \ ... rest of the arguments ... 2. Once QEMU starts, but before guest reaches the point where FEC deriver is done initializing the HW, Guest, via TAP interface, receives a number of multicast MDNS packets from Host (not necessarily true for every OS, but it happens at least on Fedora 25) 3. Recieving a packet in such a state results in imx_eth_can_receive() returning '0', which in turn causes tap_send() to disable corresponding event (tap.c:203) 4. Once Guest's driver reaches the point where it is ready to recieve packets it prepares Rx ring descriptors and writes ENET_RDAR_RDAR to ENET_RDAR register to indicate to HW that more descriptors are ready. And at this points emulation layer does this: s->regs[index] = ENET_RDAR_RDAR; imx_eth_enable_rx(s); which, combined with: if (!s->regs[ENET_RDAR]) { qemu_flush_queued_packets(qemu_get_queue(s->nic)); } results in Rx queue never being flushed and corresponding I/O event beign disabled. To prevent the problem, change the code to always flush packet queue when ENET_RDAR transitions 0 -> ENET_RDAR_RDAR. Cc: Peter Maydell Cc: Jason Wang Cc: Philippe Mathieu-Daudé Cc: qemu-devel@nongnu.org Cc: qemu-arm@nongnu.org Cc: yurovsky@gmail.com Reviewed-by: Peter Maydell Signed-off-by: Andrey Smirnov Signed-off-by: Peter Maydell --- hw/net/imx_fec.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) (limited to 'hw') diff --git a/hw/net/imx_fec.c b/hw/net/imx_fec.c index 8b2e4b8..eb034ff 100644 --- a/hw/net/imx_fec.c +++ b/hw/net/imx_fec.c @@ -533,7 +533,7 @@ static void imx_eth_do_tx(IMXFECState *s) } } -static void imx_eth_enable_rx(IMXFECState *s) +static void imx_eth_enable_rx(IMXFECState *s, bool flush) { IMXFECBufDesc bd; bool rx_ring_full; @@ -544,7 +544,7 @@ static void imx_eth_enable_rx(IMXFECState *s) if (rx_ring_full) { FEC_PRINTF("RX buffer full\n"); - } else if (!s->regs[ENET_RDAR]) { + } else if (flush) { qemu_flush_queued_packets(qemu_get_queue(s->nic)); } @@ -807,7 +807,7 @@ static void imx_eth_write(void *opaque, hwaddr offset, uint64_t value, if (s->regs[ENET_ECR] & ENET_ECR_ETHEREN) { if (!s->regs[index]) { s->regs[index] = ENET_RDAR_RDAR; - imx_eth_enable_rx(s); + imx_eth_enable_rx(s, true); } } else { s->regs[index] = 0; @@ -930,7 +930,7 @@ static int imx_eth_can_receive(NetClientState *nc) FEC_PRINTF("\n"); - return s->regs[ENET_RDAR] ? 1 : 0; + return !!s->regs[ENET_RDAR]; } static ssize_t imx_fec_receive(NetClientState *nc, const uint8_t *buf, @@ -1020,7 +1020,7 @@ static ssize_t imx_fec_receive(NetClientState *nc, const uint8_t *buf, } } s->rx_descriptor = addr; - imx_eth_enable_rx(s); + imx_eth_enable_rx(s, false); imx_eth_update(s); return len; } @@ -1116,7 +1116,7 @@ static ssize_t imx_enet_receive(NetClientState *nc, const uint8_t *buf, } } s->rx_descriptor = addr; - imx_eth_enable_rx(s); + imx_eth_enable_rx(s, false); imx_eth_update(s); return len; } -- cgit v1.1