netdev - Re: [PATCH net-next] rds: rely on IB/core to determine if device is ODP capable

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Message-ID: <20250408191138.GF199604@unreal>
Date: Tue, 8 Apr 2025 22:11:38 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: Allison Henderson <allison.henderson@...cle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	linux-rdma@...r.kernel.org, netdev@...r.kernel.org,
	rds-devel@....oracle.com
Subject: Re: [PATCH net-next] rds: rely on IB/core to determine if device is
 ODP capable

On Tue, Apr 08, 2025 at 09:38:14AM -0300, Jason Gunthorpe wrote:
> On Tue, Apr 08, 2025 at 03:34:13PM +0300, Leon Romanovsky wrote:
> > On Tue, Apr 08, 2025 at 09:23:38AM -0300, Jason Gunthorpe wrote:
> > > On Tue, Apr 08, 2025 at 02:04:55PM +0300, Leon Romanovsky wrote:
> > > > diff --git a/net/rds/ib.c b/net/rds/ib.c
> > > > index 9826fe7f9d00..c62aa2ff4963 100644
> > > > --- a/net/rds/ib.c
> > > > +++ b/net/rds/ib.c
> > > > @@ -153,14 +153,6 @@ static int rds_ib_add_one(struct ib_device *device)
> > > >  	rds_ibdev->max_wrs = device->attrs.max_qp_wr;
> > > >  	rds_ibdev->max_sge = min(device->attrs.max_send_sge, RDS_IB_MAX_SGE);
> > > >  
> > > > -	rds_ibdev->odp_capable =
> > > > -		!!(device->attrs.kernel_cap_flags &
> > > > -		   IBK_ON_DEMAND_PAGING) &&
> > > > -		!!(device->attrs.odp_caps.per_transport_caps.rc_odp_caps &
> > > > -		   IB_ODP_SUPPORT_WRITE) &&
> > > > -		!!(device->attrs.odp_caps.per_transport_caps.rc_odp_caps &
> > > > -		   IB_ODP_SUPPORT_READ);
> > > 
> > > This patch seems to drop the check for WRITE and READ support on the
> > > ODP.
> > 
> > Right, and they are part of IBK_ON_DEMAND_PAGING support. All ODP
> > providers support both IB_ODP_SUPPORT_WRITE and IB_ODP_SUPPORT_READ.
> 
> Where? mlx5 reads this from FW and I don't see anything blocking
> IBK_ON_DEMAND_PAGING if the FW is weird.

As the one who added it, I can assure you that we added these checks not
because of weird FW, but because these caps existed.

RDS calls to ib_reg_user_mr() with the following access_flags.

  564                 int access_flags =
  565                         (IB_ACCESS_LOCAL_WRITE | IB_ACCESS_REMOTE_READ |
  566                          IB_ACCESS_REMOTE_WRITE | IB_ACCESS_REMOTE_ATOMIC |
  567                          IB_ACCESS_ON_DEMAND);
  <...>
  575
  576                 ib_mr = ib_reg_user_mr(rds_ibdev->pd, start, length, virt_addr,
  577                                        access_flags);

If for some reason ODP doesn't support WRITE and/or READ, ib_reg_user_mr() will return an error from FW,

Thanks


> 
> Jason