netdev - Re: [PATCHv4 bpf-next 1/2] xdp: add a new helper for dev map multicast support

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Date:   Fri, 12 Jun 2020 16:54:08 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Jiri Benc <jbenc@...hat.com>,
        Eelco Chaudron <echaudro@...hat.com>, ast@...nel.org,
        Daniel Borkmann <daniel@...earbox.net>,
        Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
Subject: Re: [PATCHv4 bpf-next 1/2] xdp: add a new helper for dev map
 multicast support

On Wed, Jun 10, 2020 at 12:18:59PM +0200, Jesper Dangaard Brouer wrote:
> On Tue, 26 May 2020 22:05:38 +0800
> Hangbin Liu <liuhangbin@...il.com> wrote:
> 
> > diff --git a/net/core/xdp.c b/net/core/xdp.c
> > index 90f44f382115..acdc63833b1f 100644
> > --- a/net/core/xdp.c
> > +++ b/net/core/xdp.c
> > @@ -475,3 +475,29 @@ void xdp_warn(const char *msg, const char *func, const int line)
> >  	WARN(1, "XDP_WARN: %s(line:%d): %s\n", func, line, msg);
> >  };
> >  EXPORT_SYMBOL_GPL(xdp_warn);
> > +
> > +struct xdp_frame *xdpf_clone(struct xdp_frame *xdpf)
> > +{
> > +	unsigned int headroom, totalsize;
> > +	struct xdp_frame *nxdpf;
> > +	struct page *page;
> > +	void *addr;
> > +
> > +	headroom = xdpf->headroom + sizeof(*xdpf);
> > +	totalsize = headroom + xdpf->len;
> > +
> > +	if (unlikely(totalsize > PAGE_SIZE))
> > +		return NULL;
> > +	page = dev_alloc_page();
> > +	if (!page)
> > +		return NULL;
> > +	addr = page_to_virt(page);
> > +
> > +	memcpy(addr, xdpf, totalsize);
> 
> I don't think this will work.  You are assuming that the memory model
> (xdp_mem_info) is the same.
> 
> You happened to use i40, that have MEM_TYPE_PAGE_SHARED, and you should
> have changed this to MEM_TYPE_PAGE_ORDER0, but it doesn't crash as they
> are compatible.  If you were using mlx5, I suspect that this would
> result in memory leaking.

Is there anything else I should do except add the following line?
	nxdpf->mem.type = MEM_TYPE_PAGE_ORDER0;
> 
> You also need to update xdpf->frame_sz, as you also cannot assume it is
> the same.

Won't the memcpy() copy xdpf->frame_sz to nxdpf? 

And I didn't see xdpf->frame_sz is set in xdp_convert_zc_to_xdp_frame(),
do we need a fix?

Thanks
Hangbin
> 
> > +
> > +	nxdpf = addr;
> > +	nxdpf->data = addr + headroom;
> > +
> > +	return nxdpf;
> > +}
> > +EXPORT_SYMBOL_GPL(xdpf_clone);
> 
> 
> -- 
> Best regards,
>   Jesper Dangaard Brouer
>   MSc.CS, Principal Kernel Engineer at Red Hat
>   LinkedIn: http://www.linkedin.com/in/brouer
> 
> 
> struct xdp_frame {
> 	void *data;
> 	u16 len;
> 	u16 headroom;
> 	u32 metasize:8;
> 	u32 frame_sz:24;
> 	/* Lifetime of xdp_rxq_info is limited to NAPI/enqueue time,
> 	 * while mem info is valid on remote CPU.
> 	 */
> 	struct xdp_mem_info mem;
> 	struct net_device *dev_rx; /* used by cpumap */
> };
>