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

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Message-ID: <ZB2VNg7yVxAjJEMV@boxer>
Date:   Fri, 24 Mar 2023 13:19:02 +0100
From:   Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To:     Nuno Gonçalves <nunog@...4.com>
CC:     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, 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.

> 
>  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
>