Re: [PATCH net-next] selftests/xsk: preserve UMEM view in bidi test

[Jakub Sitnicki <jakub@cloudflare.com>]

On Tue, Jun 23, 2026 at 11:10 AM +02, Maciej Fijalkowski wrote:
> The UMEM state refactor made __send_pkts() use xsk->umem for Tx
> address generation. At the same time, the shared-UMEM Tx setup copies the
> Rx UMEM state into a Tx-local state object and resets base_addr and
> next_buffer before configuring the Tx socket.
>
> Passing that Tx-local object to xsk_configure() makes xsk->umem point to
> the zero-based Tx allocator state. This breaks the BIDIRECTIONAL test once
> the roles are switched: the same socket is then used for Rx validation, but
> received descriptors from the other logical UMEM half are checked against
> base_addr == 0. With the new UMEM bounds check, a valid address such as
> base_addr + XDP_PACKET_HEADROOM is rejected as being outside the UMEM
> window.
>
> Keep xsk->umem as the shared/Rx UMEM view used for socket configuration
> and Rx validation. Use the ifobject-local UMEM copy only for Tx descriptor
> address generation, preserving the BIDIRECTIONAL test's intent of using
> the proper logical UMEM half after the direction switch.
>
> Fixes: b17631032769 ("selftests/xsk: Move UMEM state from ifobject to xsk_socket_info")
> Signed-off-by: Maciej Fijalkowski maciej.fijalkowski@intel.com
> ---
>  tools/testing/selftests/bpf/prog_tests/test_xsk.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/test_xsk.c b/tools/testing/selftests/bpf/prog_tests/test_xsk.c
> index d8a1c0d40e5a..50a8dbacb63d 100644
> --- a/tools/testing/selftests/bpf/prog_tests/test_xsk.c
> +++ b/tools/testing/selftests/bpf/prog_tests/test_xsk.c
> @@ -1169,8 +1169,8 @@ static int receive_pkts(struct test_spec *test)
>  static int __send_pkts(struct ifobject *ifobject, struct xsk_socket_info *xsk, bool timeout)
>  {
>  	u32 i, idx = 0, valid_pkts = 0, valid_frags = 0, buffer_len;
> +	struct xsk_umem_info *umem = ifobject->xsk_arr[0].umem_real;
>  	struct pkt_stream *pkt_stream = xsk->pkt_stream;
> -	struct xsk_umem_info *umem = xsk->umem;
>  	bool use_poll = ifobject->use_poll;
>  	struct pollfd fds = { };
>  	int ret;

IIUC, this works because umem_real happens to point at shared/Tx UMEM
view (base_addr=0).

> @@ -1524,7 +1524,7 @@ static int thread_common_ops_tx(struct test_spec *test, struct ifobject *ifobjec
>  	umem_tx->base_addr = 0;
>  	umem_tx->next_buffer = 0;
>  
> -	ret = xsk_configure(test, ifobject, umem_tx, true);
> +	ret = xsk_configure(test, ifobject, umem_rx, true);
>  	if (ret)
>  		return ret;
>  	ifobject->xsk = &ifobject->xsk_arr[0];

And this bit works because thread_common_ops_tx is only invoked in
shared test case.

Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>