From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59200) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZWLs0-0004jW-Ey for qemu-devel@nongnu.org; Mon, 31 Aug 2015 05:59:21 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZWLrw-00035n-Fk for qemu-devel@nongnu.org; Mon, 31 Aug 2015 05:59:20 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48574) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZWLrw-00035d-9v for qemu-devel@nongnu.org; Mon, 31 Aug 2015 05:59:16 -0400 Received: from int-mx10.intmail.prod.int.phx2.redhat.com (int-mx10.intmail.prod.int.phx2.redhat.com [10.5.11.23]) by mx1.redhat.com (Postfix) with ESMTPS id B6877C18F722 for ; Mon, 31 Aug 2015 09:59:15 +0000 (UTC) Message-ID: <55E4256F.9010302@redhat.com> Date: Mon, 31 Aug 2015 17:59:11 +0800 From: Jason Wang MIME-Version: 1.0 References: <1440770817-20555-1-git-send-email-vyasevic@redhat.com> <1440770817-20555-3-git-send-email-vyasevic@redhat.com> In-Reply-To: <1440770817-20555-3-git-send-email-vyasevic@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v3 2/2] rtl8139: correctly track full receive buffer in standard mode List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Vladislav Yasevich , qemu-devel@nongnu.org Cc: stefanha@redhat.com On 08/28/2015 10:06 PM, Vladislav Yasevich wrote: > In standard operation mode, when the receive ring buffer > is full, the buffer actually appears empty to the driver since > the RxBufAddr (the location we wirte new data to) and RxBufPtr > (the location guest would stat reading from) are the same. > As a result, the call to rtl8139_RxBufferEmpty ends up > returning true indicating that the receive buffer is empty. > This would result in the next packet overwriting the recevie buffer > again and stalling receive operations. > > This patch tracks the number of unread bytes in the rxbuffer > using an unused C+ register. On every read and write, the > number is adjsted and the special case of a full buffer is also > trapped. > > The C+ register trick is used to simplify migration and not require > a new machine type. This register is not used in regular mode > and C+ mode doesn't have the same issue. > > Signed-off-by: Vladislav Yasevich > --- > hw/net/rtl8139.c | 45 +++++++++++++++++++++++++++++++++++++++++---- > 1 file changed, 41 insertions(+), 4 deletions(-) I'm not sure this can happen. For example, looks like the following check in rtl8139_do_receive(): if (avail != 0 && size + 8 >= avail) { can guarantee there's no overwriting?