Re: [Intel-wired-lan] [PATCH net-next v11 12/12] libeth: xdp: access ->pp through netmem_desc instead of page

[Byungchul Park <byungchul@sk.com>]

On Fri, Jul 18, 2025 at 01:42:38AM +0800, kernel test robot wrote:
> Hi Byungchul,
> 
> kernel test robot noticed the following build warnings:
> 
> [auto build test WARNING on c65d34296b2252897e37835d6007bbd01b255742]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Byungchul-Park/netmem-introduce-struct-netmem_desc-mirroring-struct-page/20250717-150253
> base:   c65d34296b2252897e37835d6007bbd01b255742
> patch link:    https://lore.kernel.org/r/20250717070052.6358-13-byungchul%40sk.com
> patch subject: [Intel-wired-lan] [PATCH net-next v11 12/12] libeth: xdp: access ->pp through netmem_desc instead of page
> config: arm-randconfig-r072-20250717 (https://download.01.org/0day-ci/archive/20250718/202507180111.jygqJHzk-lkp@intel.com/config)
> compiler: arm-linux-gnueabi-gcc (GCC) 8.5.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250718/202507180111.jygqJHzk-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202507180111.jygqJHzk-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):
> 
>    In file included from include/linux/container_of.h:5,
>                     from include/linux/list.h:5,
>                     from include/linux/timer.h:5,
>                     from include/linux/netdevice.h:24,
>                     from include/trace/events/xdp.h:8,
>                     from include/linux/bpf_trace.h:5,
>                     from include/net/libeth/xdp.h:7,
>                     from drivers/net/ethernet/intel/libeth/tx.c:6:
>    include/net/libeth/xdp.h: In function 'libeth_xdp_prepare_buff':
> >> include/net/libeth/xdp.h:1295:23: warning: passing argument 1 of 'page_pool_page_is_pp' discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
>         pp_page_to_nmdesc(page)->pp->p.offset, len, true);
>                           ^~~~
>    include/linux/build_bug.h:30:63: note: in definition of macro 'BUILD_BUG_ON_INVALID'
>     #define BUILD_BUG_ON_INVALID(e) ((void)(sizeof((__force long)(e))))
>                                                                   ^
>    include/net/netmem.h:301:2: note: in expansion of macro 'DEBUG_NET_WARN_ON_ONCE'
>      DEBUG_NET_WARN_ON_ONCE(!page_pool_page_is_pp(p));  \
>      ^~~~~~~~~~~~~~~~~~~~~~
>    include/net/libeth/xdp.h:1295:5: note: in expansion of macro 'pp_page_to_nmdesc'
>         pp_page_to_nmdesc(page)->pp->p.offset, len, true);
>         ^~~~~~~~~~~~~~~~~
>    In file included from arch/arm/include/asm/cacheflush.h:10,
>                     from include/linux/cacheflush.h:5,
>                     from include/linux/highmem.h:8,
>                     from include/linux/bvec.h:10,
>                     from include/linux/skbuff.h:17,
>                     from include/net/net_namespace.h:43,
>                     from include/linux/netdevice.h:38,
>                     from include/trace/events/xdp.h:8,
>                     from include/linux/bpf_trace.h:5,
>                     from include/net/libeth/xdp.h:7,
>                     from drivers/net/ethernet/intel/libeth/tx.c:6:
>    include/linux/mm.h:4176:54: note: expected 'struct page *' but argument is of type 'const struct page *'
>     static inline bool page_pool_page_is_pp(struct page *page)
>                                             ~~~~~~~~~~~~~^~~~

Oh.  page_pool_page_is_pp() in the mainline code already has this issue
that the helper cannot take const struct page * as argument.

How should we resolve the issue?  Changing page_pool_page_is_pp() to
macro and using _Generic again looks too much.  Or should we?  Any idea?

	Byungchul

> vim +1295 include/net/libeth/xdp.h
> 
>   1263
>   1264  bool libeth_xdp_buff_add_frag(struct libeth_xdp_buff *xdp,
>   1265                                const struct libeth_fqe *fqe,
>   1266                                u32 len);
>   1267
>   1268  /**
>   1269   * libeth_xdp_prepare_buff - fill &libeth_xdp_buff with head FQE data
>   1270   * @xdp: XDP buffer to attach the head to
>   1271   * @fqe: FQE containing the head buffer
>   1272   * @len: buffer len passed from HW
>   1273   *
>   1274   * Internal, use libeth_xdp_process_buff() instead. Initializes XDP buffer
>   1275   * head with the Rx buffer data: data pointer, length, headroom, and
>   1276   * truesize/tailroom. Zeroes the flags.
>   1277   * Uses faster single u64 write instead of per-field access.
>   1278   */
>   1279  static inline void libeth_xdp_prepare_buff(struct libeth_xdp_buff *xdp,
>   1280                                             const struct libeth_fqe *fqe,
>   1281                                             u32 len)
>   1282  {
>   1283          const struct page *page = __netmem_to_page(fqe->netmem);
>   1284
>   1285  #ifdef __LIBETH_WORD_ACCESS
>   1286          static_assert(offsetofend(typeof(xdp->base), flags) -
>   1287                        offsetof(typeof(xdp->base), frame_sz) ==
>   1288                        sizeof(u64));
>   1289
>   1290          *(u64 *)&xdp->base.frame_sz = fqe->truesize;
>   1291  #else
>   1292          xdp_init_buff(&xdp->base, fqe->truesize, xdp->base.rxq);
>   1293  #endif
>   1294          xdp_prepare_buff(&xdp->base, page_address(page) + fqe->offset,
> > 1295                           pp_page_to_nmdesc(page)->pp->p.offset, len, true);
>   1296  }
>   1297
> 
> --
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki