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From e5cdc492ec39f777b0bd877ca794f3b2ccdcffec Mon Sep 17 00:00:00 2001
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From: Stefan Hajnoczi <stefanha@redhat.com>
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Date: Wed, 22 May 2013 14:50:18 +0200
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Subject: [PATCH] rtl8139: flush queued packets when RxBufPtr is written
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Net queues support efficient "receive disable". For example, tap's file
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descriptor will not be polled while its peer has receive disabled. This
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saves CPU cycles for needlessly copying and then dropping packets which
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the peer cannot receive.
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rtl8139 is missing the qemu_flush_queued_packets() call that wakes the
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queue up when receive becomes possible again.
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As a result, the Windows 7 guest driver reaches a state where the
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rtl8139 cannot receive packets. The driver has actually refilled the
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receive buffer but we never resume reception.
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The bug can be reproduced by running a large FTP 'get' inside a Windows
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7 guest:
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$ qemu -netdev tap,id=tap0,...
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-device rtl8139,netdev=tap0
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The Linux guest driver does not trigger the bug, probably due to a
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different buffer management strategy.
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Reported-by: Oliver Francke <oliver.francke@filoo.de>
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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(cherry picked from commit 00b7ade807b5ce6779ddd86ce29c5521ec5c529a)
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---
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hw/rtl8139.c | 3 +++
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1 file changed, 3 insertions(+)
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diff --git a/hw/rtl8139.c b/hw/rtl8139.c
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index d7716be..2c4d9bd 100644
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--- a/hw/rtl8139.c
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+++ b/hw/rtl8139.c
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@@ -2575,6 +2575,9 @@ static void rtl8139_RxBufPtr_write(RTL8139State *s, uint32_t val)
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/* this value is off by 16 */
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s->RxBufPtr = MOD2(val + 0x10, s->RxBufferSize);
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+ /* more buffer space may be available so try to receive */
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+ qemu_flush_queued_packets(qemu_get_queue(s->nic));
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+
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DPRINTF(" CAPR write: rx buffer length %d head 0x%04x read 0x%04x\n",
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s->RxBufferSize, s->RxBufAddr, s->RxBufPtr);
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}
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