netdev - Re: [PATCH bpf-next V4] xsk: allow remap of fill and/or completion rings

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Message-ID: <CAJ8uoz3f1=MPiranw7iU0DWNuBka4g7hNn5POgoFVHbOkun8OQ@mail.gmail.com>
Date:   Fri, 24 Mar 2023 14:30:17 +0100
From:   Magnus Karlsson <magnus.karlsson@...il.com>
To:     Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Cc:     Nuno Gonçalves <nunog@...4.com>,
        Björn Töpel <bjorn@...nel.org>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Christian Brauner <brauner@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next V4] xsk: allow remap of fill and/or completion rings

On Fri, 24 Mar 2023 at 13:22, Maciej Fijalkowski
<maciej.fijalkowski@...el.com> wrote:
>
> On Fri, Mar 24, 2023 at 10:02:22AM +0000, Nuno Gonçalves wrote:
> > The remap of fill and completion rings was frowned upon as they
> > control the usage of UMEM which does not support concurrent use.
> > At the same time this would disallow the remap of these rings
> > into another process.
> >
> > A possible use case is that the user wants to transfer the socket/
> > UMEM ownership to another process (via SYS_pidfd_getfd) and so
> > would need to also remap these rings.
> >
> > This will have no impact on current usages and just relaxes the
> > remap limitation.
> >
> > Signed-off-by: Nuno Gonçalves <nunog@...4.com>
> > ---
> > V3 -> V4: Remove undesired format changes
> > V2 -> V3: Call READ_ONCE for each variable and not for the ternary operator
> > V1 -> V2: Format and comment changes
>
> thanks, it now looks good to me, i applied this locally and it builds, so:
> Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
>
> but i am giving a last call to Magnus since he was acking this before.

I have already acked it, but I can do it twice.
Acked-by: Magnus Karlsson <magnus.karlsson@...el.com>

> >
> >  net/xdp/xsk.c | 9 ++++++---
> >  1 file changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> > index 2ac58b282b5eb..cc1e7f15fa731 100644
> > --- a/net/xdp/xsk.c
> > +++ b/net/xdp/xsk.c
> > @@ -1301,9 +1301,10 @@ static int xsk_mmap(struct file *file, struct socket *sock,
> >       loff_t offset = (loff_t)vma->vm_pgoff << PAGE_SHIFT;
> >       unsigned long size = vma->vm_end - vma->vm_start;
> >       struct xdp_sock *xs = xdp_sk(sock->sk);
> > +     int state = READ_ONCE(xs->state);
> >       struct xsk_queue *q = NULL;
> >
> > -     if (READ_ONCE(xs->state) != XSK_READY)
> > +     if (state != XSK_READY && state != XSK_BOUND)
> >               return -EBUSY;
> >
> >       if (offset == XDP_PGOFF_RX_RING) {
> > @@ -1314,9 +1315,11 @@ static int xsk_mmap(struct file *file, struct socket *sock,
> >               /* Matches the smp_wmb() in XDP_UMEM_REG */
> >               smp_rmb();
> >               if (offset == XDP_UMEM_PGOFF_FILL_RING)
> > -                     q = READ_ONCE(xs->fq_tmp);
> > +                     q = state == XSK_READY ? READ_ONCE(xs->fq_tmp) :
> > +                                              READ_ONCE(xs->pool->fq);
> >               else if (offset == XDP_UMEM_PGOFF_COMPLETION_RING)
> > -                     q = READ_ONCE(xs->cq_tmp);
> > +                     q = state == XSK_READY ? READ_ONCE(xs->cq_tmp) :
> > +                                              READ_ONCE(xs->pool->cq);
> >       }
> >
> >       if (!q)
> > --
> > 2.40.0
> >