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

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Date:   Mon, 20 Mar 2023 13:03:14 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Nuno Gonçalves <nunog@...4.com>
Cc:     Björn Töpel <bjorn@...nel.org>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...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] xsk: allow remap of fill and/or completion rings

On Mon, Mar 20, 2023 at 10:53:23AM +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 this rings
> into another process.
> 
> A possible use case is that the user wants to transfer the socket/
> UMEM ownerwhip to another process (via SYS_pidfd_getfd) and so
> would need to also remap this rings.
> 
> This will have no impact on current usages and just relaxes the
> remap limitation.
> 
> Signed-off-by: Nuno Gonçalves <nunog@...4.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..2af4ff64b22bd 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -1300,10 +1300,11 @@ 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;
> +	int state = READ_ONCE(xs->state);
>  	struct xdp_sock *xs = xdp_sk(sock->sk);
>  	struct xsk_queue *q = NULL;
>  
> -	if (READ_ONCE(xs->state) != XSK_READY)
> +	if (!(state == XSK_READY || state == XSK_BOUND))

This if(..) is actually:
 if (state != XSK_READY && state != XSK_BOUND)

Thanks