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

Jesper Dangaard Brouer
2020-06-10T10:19:18Z

On Tue, 26 May 2020 22:05:38 +0800
Hangbin Liu <liuhangbin@gmail.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.

You also need to update xdpf->frame_sz, as you also cannot assume it is
the same.

> +
> + 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 */
};