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

Hangbin Liu
2020-06-12T08:54:23Z

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@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.

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 */
> };
>