[dpdk-dev] [PATCH] vhost: fix host notifier configuration error flow

[Matan Azrad]

Hi Xia
Thanks for the fast review.
Please see inline.

From: Xia, Chenbo:
> Hi Matan,
> 
> > -----Original Message-----
> > From: dev <dev-bounces at dpdk.org> On Behalf Of Matan Azrad
> > Sent: Thursday, June 11, 2020 11:48 PM
> > To: Maxime Coquelin <maxime.coquelin at redhat.com>
> > Cc: dev at dpdk.org; Wang, Xiao W <xiao.w.wang at intel.com>; Tiwei Bie
> > <tiwei.bie at intel.com>; stable at dpdk.org
> > Subject: [dpdk-dev] [PATCH] vhost: fix host notifier configuration
> > error flow
> >
> > A vDPA driver can configure its device FD to be notified directly by
> > the guest memory mapping using `rte_vhost_host_notifier_ctrl` API.
> >
> > The driver request is managed by the dpdk vhost management and is
> > forwarded to the QEMU, the vhost massage includes reply request in
> > order to be sure that the memory mapping was done correctly by the
> QEMU.
> >
> > When QEMU finishes the configuration, it marks that its replay is
> > valid in the slave FD using VHOST_USER_REPLY_MASK flag.
> > The flag is set only in success and when the slave FD includes the reply
> data.
> >
> > The vhost library didn't validate the above flag before accessing to
> > the slave FD, it leaded to the thread to be blocked on recvmsg call
> > forever in case the QEMU has some problems in the notifier configuration.
> >
> > Handle VHOST_USER_REPLY_MASK flag to validate that slave FD includes a
> > reply data.
> >
> > Fixes: d90cf7d111ac ("vhost: support host notifier")
> > Cc: stable at dpdk.org
> >
> > Signed-off-by: Matan Azrad <matan at mellanox.com>
> > ---
> >  lib/librte_vhost/vhost_user.c | 10 ++++++++--
> >  1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/lib/librte_vhost/vhost_user.c
> > b/lib/librte_vhost/vhost_user.c index
> > 84bebad..aa19d15 100644
> > --- a/lib/librte_vhost/vhost_user.c
> > +++ b/lib/librte_vhost/vhost_user.c
> > @@ -2833,8 +2833,14 @@ static int process_slave_message_reply(struct
> > virtio_net *dev,
> >  	struct VhostUserMsg msg_reply;
> >  	int ret;
> >
> > -	if ((msg->flags & VHOST_USER_NEED_REPLY) == 0)
> > -		return 0;
> > +	if (!(msg->flags & VHOST_USER_REPLY_MASK)) {
> > +		if (msg->flags & VHOST_USER_NEED_REPLY) {
> > +			ret = -1;
> > +			goto out;
> > +		} else {
> > +			return 0;
> > +		}
> > +	}
> 
> Based on your commit log, I think you want to check the reply msg sent from
> qemu but msg is the request sent from vhost-user.

Yes, looks like I missed here something.

> 
> Also, could you clarify the problem based on that? Because I see in QEMU
> v5.0.0 that if vhost request has VHOST_USER_NEED_REPLY_MASK, qemu will
> set the reply mask with VHOST_USER_REPLY_MASK and without
> VHOST_USER_NEED_REPLY_MASK no matter the handle is correct. Do I miss
> something? Please correct me.

I got stuck in this function while receiving massage back from QEMU(4.2.0).
Looks like QEMU printed "Failed to read from slave. ".
In this case looks like QEMU doesn't reply and therefore the dpdk thread was stuck.
Any idea?




> Thanks!
> Chenbo
> 
> >
> >  	ret = read_vhost_message(dev->slave_req_fd, &msg_reply);
> >  	if (ret <= 0) {
> > --
> > 1.8.3.1