linux-kernel - Re: [PATCH] IB/mlx5: unify return value to ENOENT

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Date:   Wed, 13 Oct 2021 15:02:12 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "lizhijian@...itsu.com" <lizhijian@...itsu.com>
Cc:     "leon@...nel.org" <leon@...nel.org>,
        "dledford@...hat.com" <dledford@...hat.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] IB/mlx5: unify return value to ENOENT

On Wed, Oct 13, 2021 at 07:26:49AM +0000, lizhijian@...itsu.com wrote:
> Hi Jason
> 
> When update the ibv_advise_mr man page, i have a few concerns:
> 
> 
> On 29/09/2021 01:08, Jason Gunthorpe wrote:
> > On Fri, Sep 03, 2021 at 04:48:15PM +0800, Li Zhijian wrote:
> >> Previously, ENOENT or EINVAL will be returned by ibv_advise_mr() although
> >> the errors all occur at get_prefetchable_mr().
> > What do you think about this instead?
> >
> >  From b739920ed4869decb02a0dbc58256e6c72ec7061 Mon Sep 17 00:00:00 2001
> > From: Jason Gunthorpe <jgg@...dia.com>
> > Date: Fri, 3 Sep 2021 16:48:15 +0800
> > Subject: [PATCH] IB/mlx5: Flow through a more detailed return code from
> >   get_prefetchable_mr()
> >
> > The error returns for various cases detected by get_prefetchable_mr() get
> > confused as it flows back to userspace. Properly label each error path and
> > flow the error code properly back to the system call.
> >
> > Suggested-by: Li Zhijian <lizhijian@...fujitsu.com>
> > Signed-off-by: Jason Gunthorpe <jgg@...dia.com>
> >   drivers/infiniband/hw/mlx5/odp.c | 40 ++++++++++++++++++++------------
> >   1 file changed, 25 insertions(+), 15 deletions(-)
> >
> > diff --git a/drivers/infiniband/hw/mlx5/odp.c b/drivers/infiniband/hw/mlx5/odp.c
> > index d0d98e584ebcc3..77890a85fc2dd3 100644
> > +++ b/drivers/infiniband/hw/mlx5/odp.c
> > @@ -1708,20 +1708,26 @@ get_prefetchable_mr(struct ib_pd *pd, enum ib_uverbs_advise_mr_advice advice,
> >   
> >   	xa_lock(&dev->odp_mkeys);
> >   	mmkey = xa_load(&dev->odp_mkeys, mlx5_base_mkey(lkey));
> > -	if (!mmkey || mmkey->key != lkey || mmkey->type != MLX5_MKEY_MR)
> > +	if (!mmkey || mmkey->key != lkey) {
> > +		mr = ERR_PTR(-ENOENT);
> >   		goto end;
> > +	}
> > +	if (mmkey->type != MLX5_MKEY_MR) {
> > +		mr = ERR_PTR(-EINVAL);
> > +		goto end;
> > +	}
> 
> 
> Can we return EINVAL in both above 2 cases so that we can attribute
> them to *lkey is invalid*  simply.  Otherwise it's hard to describe
> 2nd case by man page since users/developers cannot link mmkey->type
> to the parameters of ibv_advise_mr().

kley is valid in the 2nd case, but points to the wrong kidn of object
to prefetch, hence EIVNAL. Eg it is a MW or something.

> >   	mr = container_of(mmkey, struct mlx5_ib_mr, mmkey);
> >   
> >   	if (mr->ibmr.pd != pd) {
> > -		mr = NULL;
> > +		mr = ERR_PTR(-EPERM);
> 
> EINVAL is better  for compatible ? since man page said EINVAL in this case before.

Referencing a valid lkey outside the caller's security scope should be
EPERM.

Jason