linux-kernel - Re: [PATCH rdma-next 1/1] RDMA/mana_ib: indicate that inline data is not supported

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Message-ID:
 <PAXPR83MB05595BBC92EB695753EB8563B4A22@PAXPR83MB0559.EURPRD83.prod.outlook.com>
Date: Tue, 16 Jul 2024 14:55:26 +0000
From: Konstantin Taranov <kotaranov@...rosoft.com>
To: Leon Romanovsky <leon@...nel.org>
CC: Konstantin Taranov <kotaranov@...ux.microsoft.com>, Wei Hu
	<weh@...rosoft.com>, "sharmaajay@...rosoft.com" <sharmaajay@...rosoft.com>,
	Long Li <longli@...rosoft.com>, "jgg@...pe.ca" <jgg@...pe.ca>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH rdma-next 1/1] RDMA/mana_ib: indicate that inline data is
 not supported

> > > > Set max_inline_data to zero during RC QP creation.
> > > >
> > > > Fixes: fdefb9184962 ("RDMA/mana_ib: Implement uapi to create and
> > > > destroy RC QP")
> > > > Signed-off-by: Konstantin Taranov <kotaranov@...rosoft.com>
> > > > ---
> > > >  drivers/infiniband/hw/mana/qp.c | 2 ++
> > > >  1 file changed, 2 insertions(+)
> > > >
> > > > diff --git a/drivers/infiniband/hw/mana/qp.c
> > > > b/drivers/infiniband/hw/mana/qp.c index 73d67c853b6f..d9f24a763e72
> > > > 100644
> > > > --- a/drivers/infiniband/hw/mana/qp.c
> > > > +++ b/drivers/infiniband/hw/mana/qp.c
> > > > @@ -426,6 +426,8 @@ static int mana_ib_create_rc_qp(struct ib_qp
> > > > *ibqp,
> > > struct ib_pd *ibpd,
> > > >  	u64 flags = 0;
> > > >  	u32 doorbell;
> > > >
> > > > +	/* inline data is not supported */
> > > > +	attr->cap.max_inline_data = 0;
> > >
> > > Can you please point to me to the flow where attr is not zeroed before?
> > >
> >
> > Sorry, I do not understand the question. I cannot point to something that is
> not in the code.
> >
> > It is to support the case when user asks for x bytes inlined when it
> > creates a QP, and we respond with actual allowed inline data for the
> > created QP. (as defined in: "The function ibv_create_qp() will update
> > the qp_init_attr->cap struct with the actual QP values of the QP that
> > was created;")
> >
> > The kernel logic is inside "static int create_qp(struct uverbs_attr_bundle
> *attrs, struct ib_uverbs_ex_create_qp *cmd)"
> > where we do the following:
> > attr.cap.max_inline_data = cmd->max_inline_data; qp =
> > ib_create_qp_user(..,&attr,..);
> 
> Awesome, ib_create_qp_user() is called exactly in two places, and in both
> cases I see this line "struct ib_qp_init_attr attr = {}; "
> 
> It means that attr is zeroed.
> 

I think there is some misunderstanding.
So, the attr is zeroed at init. Then it is filled with values from the user request.
With
	attr.cap.max_send_wr     = cmd->max_send_wr;
	attr.cap.max_recv_wr     = cmd->max_recv_wr;
	attr.cap.max_send_sge    = cmd->max_send_sge;
	attr.cap.max_recv_sge    = cmd->max_recv_sge;
	attr.cap.max_inline_data = cmd->max_inline_data;
or with:
	set_caps(&attr, &cap, true);

So at this moment there is a value from the user in the attr (it is not 0).
ib_create_qp_user is called with the attr.

The drivers are allowed to tune the cap values during QP create.
So I want to set it to 0 as some other provides (see pvrdma_create_qp,
rvt_create_qp, set_kernel_sq_size from mlx4).

After the driver call has happened, the modified cap value are copied to temp variable:
	resp.base.max_recv_sge    = attr.cap.max_recv_sge;
	resp.base.max_send_sge    = attr.cap.max_send_sge;
	resp.base.max_recv_wr     = attr.cap.max_recv_wr;
	resp.base.max_send_wr     = attr.cap.max_send_wr;
	resp.base.max_inline_data = attr.cap.max_inline_data;
or with:
	set_caps(&attr, &cap, false);
And then copied to the user with:
	uverbs_response(attrs, &resp, sizeof(resp));
or with
	uverbs_copy_to_struct_or_zero(attrs,
					UVERBS_ATTR_CREATE_QP_RESP_CAP, &cap,
					sizeof(cap));

Do you agree that my patch solves a problem in mana_ib (there is no problem in core)?
Or do you think that I am trying to solve non-existent problem?

Thanks

> Thanks
> 
> > resp.base.max_inline_data = attr.cap.max_inline_data;
> >
> > So, my change makes sure that the response will have 0 and not the
> > value the user asked, as we do not support inlining. So without the
> > fix, the user who was asking for inlining was falsely seeing that we support
> it (example of such an application is rdma_server from librdmacm).
> >
> > Thanks
> >
> > > Thanks
> > >
> > > >  	if (!udata || udata->inlen < sizeof(ucmd))
> > > >  		return -EINVAL;
> > > >
> > > > --
> > > > 2.43.0
> > > >