netdev - Re: [PATCH rdma-next 2/5] RDMA/core: Don't depend device ODP capabilities on kconfig option

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Date:   Thu, 20 Dec 2018 17:33:11 +0000
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     Leon Romanovsky <leon@...nel.org>
CC:     Doug Ledford <dledford@...hat.com>,
        RDMA mailing list <linux-rdma@...r.kernel.org>,
        Haggai Eran <haggaie@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        linux-netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH rdma-next 2/5] RDMA/core: Don't depend device ODP
 capabilities on kconfig option

On Thu, Dec 20, 2018 at 07:29:56PM +0200, Leon Romanovsky wrote:
> On Thu, Dec 20, 2018 at 05:20:51PM +0000, Jason Gunthorpe wrote:
> > On Thu, Dec 20, 2018 at 11:23:15AM +0200, Leon Romanovsky wrote:
> > > From: Leon Romanovsky <leonro@...lanox.com>
> > >
> > > Device capability bits are exposing what specific device supports from
> > > HW perspective. Those bits are not dependent on kernel configurations
> > > and RDMA/core should ensure that proper interfaces to users will be
> > > disabled if CONFIG_INFINIBAND_ON_DEMAND_PAGING is not set.
> > >
> > > Fixes: f4056bfd8ccf ("IB/core: Add on demand paging caps to ib_uverbs_ex_query_device")
> > > Fixes: 8cdd312cfed7 ("IB/mlx5: Implement the ODP capability query verb")
> > > Signed-off-by: Leon Romanovsky <leonro@...lanox.com>
> > >  drivers/infiniband/core/uverbs_cmd.c | 2 --
> > >  drivers/infiniband/hw/mlx5/main.c    | 2 --
> > >  2 files changed, 4 deletions(-)
> > >
> > > diff --git a/drivers/infiniband/core/uverbs_cmd.c b/drivers/infiniband/core/uverbs_cmd.c
> > > index 6b12cc5f97b2..549d9eedf62e 100644
> > > +++ b/drivers/infiniband/core/uverbs_cmd.c
> > > @@ -3609,7 +3609,6 @@ static int ib_uverbs_ex_query_device(struct uverbs_attr_bundle *attrs)
> > >
> > >  	copy_query_dev_fields(ucontext, &resp.base, &attr);
> > >
> > > -#ifdef CONFIG_INFINIBAND_ON_DEMAND_PAGING
> > >  	resp.odp_caps.general_caps = attr.odp_caps.general_caps;
> > >  	resp.odp_caps.per_transport_caps.rc_odp_caps =
> > >  		attr.odp_caps.per_transport_caps.rc_odp_caps;
> > > @@ -3617,7 +3616,6 @@ static int ib_uverbs_ex_query_device(struct uverbs_attr_bundle *attrs)
> > >  		attr.odp_caps.per_transport_caps.uc_odp_caps;
> > >  	resp.odp_caps.per_transport_caps.ud_odp_caps =
> > >  		attr.odp_caps.per_transport_caps.ud_odp_caps;
> > > -#endif
> >
> > This one is maybe OK, assuming the driver fills in 0..
> >
> > >  	resp.timestamp_mask = attr.timestamp_mask;
> > >  	resp.hca_core_clock = attr.hca_core_clock;
> > > diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
> > > index 6584e638387a..d7e5ba5034aa 100644
> > > +++ b/drivers/infiniband/hw/mlx5/main.c
> > > @@ -923,11 +923,9 @@ static int mlx5_ib_query_device(struct ib_device *ibdev,
> > >  	props->hca_core_clock = MLX5_CAP_GEN(mdev, device_frequency_khz);
> > >  	props->timestamp_mask = 0x7FFFFFFFFFFFFFFFULL;
> > >
> > > -#ifdef CONFIG_INFINIBAND_ON_DEMAND_PAGING
> > >  	if (MLX5_CAP_GEN(mdev, pg))
> > >  		props->device_cap_flags |= IB_DEVICE_ON_DEMAND_PAGING;
> > >  	props->odp_caps = dev->odp_caps;
> > > -#endif
> >
> > But shouldn't this be protected? If the driver has compiled out ODP it
> > shouldn't set the cap flag...
> 
> I see those capabilities as device properties and not as kernel ones.
> 
> Current situation looks bad for me, when I have same device which
> reports differently information depends on some compilation flag.

It is not device capabilities, it is a kernel API capability if the
API is not available the bit should not be set.

The field is badly named.

Jason