On 6 November 2017 at 15:47, Andrey Smirnov <andrew.smir...@gmail.com> wrote:
> 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 <peter.mayd...@linaro.org>
> Cc: Jason Wang <jasow...@redhat.com>
> Cc: Philippe Mathieu-Daudé <f4...@amsat.org>
> Cc: qemu-devel@nongnu.org
> Cc: qemu-...@nongnu.org
> Cc: yurov...@gmail.com
> Signed-off-by: Andrey Smirnov <andrew.smir...@gmail.com>
> diff --git a/include/hw/net/imx_fec.h b/include/hw/net/imx_fec.h
> index 62ad473b05..4bc8f03ec2 100644
> --- a/include/hw/net/imx_fec.h
> +++ b/include/hw/net/imx_fec.h
> @@ -252,6 +252,7 @@ typedef struct IMXFECState {
> uint32_t phy_int_mask;
>
> bool is_fec;
> + bool needs_flush;
> } IMXFECState;
This field isn't needed any more in this version of the patch, I think?
otherwise
Reviewed-by: Peter Maydell <peter.mayd...@linaro.org>
thanks
-- PMM
