linux-kernel - Re: [PATCH rdma-rc] RDMA/cma: Clear all multicast request fields

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Date:   Mon, 17 Jan 2022 20:20:40 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
        syzbot+8fcbb77276d43cc8b693@...kaller.appspotmail.com
Subject: Re: [PATCH rdma-rc] RDMA/cma: Clear all multicast request fields

On Mon, Jan 17, 2022 at 12:16:21PM -0400, Jason Gunthorpe wrote:
> On Mon, Jan 10, 2022 at 08:05:40PM +0200, Leon Romanovsky wrote:
> 
> > > We should probably check the PS even earlier to prevent the IB side
> > > from having the same issue.
> > 
> > What do you think about this?
> 
> IB is a bit different, it has a bunch of PS's that are UD compatible..
> 
> Probably what we really want here is to check/restrict the CM ID to
> SIDR mode, which does have the qkey and is the only mode that makes
> sense to be mixed with multicast, and then forget about port space
> entirely.
> 
> It may be that port space indirectly restricts the CM ID to SIDR mode,
> but the language here should be 'is in sidr mode', not some confusing
> open coded port space check.
> 
> I'm also not sure of the lifecycle of the qkey, qkeys only exist in
> SIDR mode so obviously anything that sets/gets a qkey should be
> restriced to SIDR CM IDs..
> 
> > diff --git a/drivers/infiniband/core/cma.c b/drivers/infiniband/core/cma.c
> > index 835ac54d4a24..0a1f008ca929 100644
> > +++ b/drivers/infiniband/core/cma.c
> > @@ -4669,12 +4669,8 @@ static int cma_join_ib_multicast(struct rdma_id_private *id_priv,
> >         if (ret)
> >                 return ret;
> > 
> > -       ret = cma_set_qkey(id_priv, 0);
> > -       if (ret)
> > -               return ret;
> > -
> >         cma_set_mgid(id_priv, (struct sockaddr *) &mc->addr, &rec.mgid);
> > -       rec.qkey = cpu_to_be32(id_priv->qkey);
> > +       rec.qkey = cpu_to_be32(RDMA_UDP_QKEY);
> 
> And I'm not sure this makes sense? The UD qkey should still be
> negotiated right?

Yes, I think so, it will be changed in SIDR phase.

The original code has "cma_set_qkey(id_priv, 0)" call, that in IB case will
execute this switch anyway:
   515         switch (id_priv->id.ps) {
   516         case RDMA_PS_UDP:
   517         case RDMA_PS_IB:
   518                 id_priv->qkey = RDMA_UDP_QKEY;

The difference is that we won't store RDMA_UDP_QKEY in id_priv->qkey,
but I'm unsure that this is right.

Thanks

> 
> Jason