[dpdk-dev] [dpdk-stable] [PATCH v4 1/6] vhost: fix windows vm hang

[Yuanhan Liu]

On Mon, Sep 05, 2016 at 05:25:31AM +0000, Wang, Zhihong wrote:
> 
> 
> > -----Original Message-----
> > From: Yuanhan Liu [mailto:yuanhan.liu at linux.intel.com]
> > Sent: Monday, September 5, 2016 1:25 PM
> > To: Wang, Zhihong <zhihong.wang at intel.com>
> > Cc: dev at dpdk.org; maxime.coquelin at redhat.com;
> > yuanhan.liu at linux.intel.com; thomas.monjalon at 6wind.com;
> > stable at dpdk.org
> > Subject: Re: [dpdk-stable] [PATCH v4 1/6] vhost: fix windows vm hang
> > 
> > On Mon, Aug 29, 2016 at 11:35:59PM -0400, Zhihong Wang wrote:
> > > This patch fixes a Windows VM compatibility issue in DPDK 16.07 vhost
> > code,
> > > which causes the guest to hang once any packets are enqueued when
> > mrg_rxbuf
> > > is turned on.
> > 
> > This commit log lacks two important pieces: why does the hang happen and
> > how does your patch fix it.
> 
> Okay, I'll add it in v5.
> 
> > 
> > > How to test?
> > >
> > >  1. Start testpmd in the host with a vhost port.
> > >
> > >  2. Start a Windows VM image with qemu and connect to the vhost port.
> > >
> > >  3. Start io forwarding with tx_first in host testpmd.
> > >
> > > For 16.07 code, the Windows VM will hang once any packets are enqueued.
> > >
> > > Cc: <stable at dpdk.org>
> > > Signed-off-by: Zhihong Wang <zhihong.wang at intel.com>
> > > ---
> > >  lib/librte_vhost/vhost_rxtx.c | 17 ++++++++++++-----
> > >  1 file changed, 12 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/lib/librte_vhost/vhost_rxtx.c b/lib/librte_vhost/vhost_rxtx.c
> > > index 08a73fd..5806f99 100644
> > > --- a/lib/librte_vhost/vhost_rxtx.c
> > > +++ b/lib/librte_vhost/vhost_rxtx.c
> > > @@ -384,6 +384,8 @@ copy_mbuf_to_desc_mergeable(struct virtio_net
> > *dev, struct vhost_virtqueue *vq,
> > >  	uint16_t start_idx = vq->last_used_idx;
> > >  	uint16_t cur_idx = start_idx;
> > >  	uint64_t desc_addr;
> > > +	uint32_t desc_chain_head;
> > > +	uint32_t desc_chain_len;
> > 
> > What's the point of introducing "desc_chain_len"? It has the same value
> > of desc_offset.
> 
> No it's not, desc_offset is the offset of the current desc only.
> That's where the old code goes wrong.

Oh, right.

	--yliu