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

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Message-ID: <20250410113505.GQ199604@unreal>
Date: Thu, 10 Apr 2025 14:35:05 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Allison Henderson <allison.henderson@...cle.com>
Cc: "jgg@...dia.com" <jgg@...dia.com>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	"rds-devel@....oracle.com" <rds-devel@....oracle.com>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"kuba@...nel.org" <kuba@...nel.org>,
	"pabeni@...hat.com" <pabeni@...hat.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] rds: rely on IB/core to determine if device is
 ODP capable

On Wed, Apr 09, 2025 at 12:54:39AM +0000, Allison Henderson wrote:
> On Tue, 2025-04-08 at 22:11 +0300, Leon Romanovsky wrote:
> > 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.
> Hi Leon,
> 
> Thanks for the patch.  Is there a commit id for the FW checks we can see?

It is part of FW checks to provided access_flags. In this case, you are
asking for IB_ACCESS_REMOTE_READ and IB_ACCESS_ON_DEMAND.

The check of IB_ODP_SUPPORT_READ is used when you need to dig which
transport actually supports it.

The thing is that ODP was always supported for RC QPs, from day one.

> Maybe we can just add a little more detail to
> the commit description to make clear where they are and what they're checking for.  Thank you!

Sure, will update it.

Thanks

> 
> Allison
> 
> > 
> > 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
>