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    Subject[PATCH net-next 18/24] net: Freescale: Use nested-BH locking for XDP redirect.
    Date
    The per-CPU variables used during bpf_prog_run_xdp() invocation and
    later during xdp_do_redirect() rely on disabled BH for their protection.
    Without locking in local_bh_disable() on PREEMPT_RT these data structure
    require explicit locking.

    This is a follow-up on the previous change which introduced
    bpf_run_lock.redirect_lock and uses it now within drivers.

    The simple way is to acquire the lock before bpf_prog_run_xdp() is
    invoked and hold it until the end of function.
    This does not always work because some drivers (cpsw, atlantic) invoke
    xdp_do_flush() in the same context.
    Acquiring the lock in bpf_prog_run_xdp() and dropping in
    xdp_do_redirect() (without touching drivers) does not work because not
    all driver, which use bpf_prog_run_xdp(), do support XDP_REDIRECT (and
    invoke xdp_do_redirect()).

    Ideally the minimal locking scope would be bpf_prog_run_xdp() +
    xdp_do_redirect() and everything else (error recovery, DMA unmapping,
    free/ alloc of memory, …) would happen outside of the locked section.

    Cc: Alexei Starovoitov <ast@kernel.org>
    Cc: Clark Wang <xiaoning.wang@nxp.com>
    Cc: Claudiu Manoil <claudiu.manoil@nxp.com>
    Cc: Ioana Ciornei <ioana.ciornei@nxp.com>
    Cc: Jesper Dangaard Brouer <hawk@kernel.org>
    Cc: John Fastabend <john.fastabend@gmail.com>
    Cc: Madalin Bucur <madalin.bucur@nxp.com>
    Cc: NXP Linux Team <linux-imx@nxp.com>
    Cc: Shenwei Wang <shenwei.wang@nxp.com>
    Cc: Vladimir Oltean <vladimir.oltean@nxp.com>
    Cc: Wei Fang <wei.fang@nxp.com>
    Cc: bpf@vger.kernel.org
    Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    ---
    .../net/ethernet/freescale/dpaa/dpaa_eth.c | 1 +
    .../net/ethernet/freescale/dpaa2/dpaa2-eth.c | 1 +
    .../net/ethernet/freescale/dpaa2/dpaa2-xsk.c | 30 ++++++++++---------
    drivers/net/ethernet/freescale/enetc/enetc.c | 1 +
    drivers/net/ethernet/freescale/fec_main.c | 1 +
    5 files changed, 20 insertions(+), 14 deletions(-)

    diff --git a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
    index dcbc598b11c6c..8adc766282fde 100644
    --- a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
    +++ b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
    @@ -2597,6 +2597,7 @@ static u32 dpaa_run_xdp(struct dpaa_priv *priv, struct qm_fd *fd, void *vaddr,
    }
    #endif

    + guard(local_lock_nested_bh)(&bpf_run_lock.redirect_lock);
    xdp_act = bpf_prog_run_xdp(xdp_prog, &xdp);

    /* Update the length and the offset of the FD */
    diff --git a/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c b/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
    index 888509cf1f210..08be35a3e3de7 100644
    --- a/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
    +++ b/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
    @@ -442,6 +442,7 @@ static u32 dpaa2_eth_run_xdp(struct dpaa2_eth_priv *priv,
    xdp_prepare_buff(&xdp, vaddr + offset, XDP_PACKET_HEADROOM,
    dpaa2_fd_get_len(fd), false);

    + guard(local_lock_nested_bh)(&bpf_run_lock.redirect_lock);
    xdp_act = bpf_prog_run_xdp(xdp_prog, &xdp);

    /* xdp.data pointer may have changed */
    diff --git a/drivers/net/ethernet/freescale/dpaa2/dpaa2-xsk.c b/drivers/net/ethernet/freescale/dpaa2/dpaa2-xsk.c
    index 051748b997f3f..e3ae9de6b0a34 100644
    --- a/drivers/net/ethernet/freescale/dpaa2/dpaa2-xsk.c
    +++ b/drivers/net/ethernet/freescale/dpaa2/dpaa2-xsk.c
    @@ -56,23 +56,25 @@ static u32 dpaa2_xsk_run_xdp(struct dpaa2_eth_priv *priv,
    xdp_buff->rxq = &ch->xdp_rxq;

    xsk_buff_dma_sync_for_cpu(xdp_buff, ch->xsk_pool);
    - xdp_act = bpf_prog_run_xdp(xdp_prog, xdp_buff);
    + scoped_guard(local_lock_nested_bh, &bpf_run_lock.redirect_lock) {
    + xdp_act = bpf_prog_run_xdp(xdp_prog, xdp_buff);

    - /* xdp.data pointer may have changed */
    - dpaa2_fd_set_offset(fd, xdp_buff->data - vaddr);
    - dpaa2_fd_set_len(fd, xdp_buff->data_end - xdp_buff->data);
    + /* xdp.data pointer may have changed */
    + dpaa2_fd_set_offset(fd, xdp_buff->data - vaddr);
    + dpaa2_fd_set_len(fd, xdp_buff->data_end - xdp_buff->data);

    - if (likely(xdp_act == XDP_REDIRECT)) {
    - err = xdp_do_redirect(priv->net_dev, xdp_buff, xdp_prog);
    - if (unlikely(err)) {
    - ch->stats.xdp_drop++;
    - dpaa2_eth_recycle_buf(priv, ch, addr);
    - } else {
    - ch->buf_count--;
    - ch->stats.xdp_redirect++;
    + if (likely(xdp_act == XDP_REDIRECT)) {
    + err = xdp_do_redirect(priv->net_dev, xdp_buff, xdp_prog);
    + if (unlikely(err)) {
    + ch->stats.xdp_drop++;
    + dpaa2_eth_recycle_buf(priv, ch, addr);
    + } else {
    + ch->buf_count--;
    + ch->stats.xdp_redirect++;
    + }
    +
    + goto xdp_redir;
    }
    -
    - goto xdp_redir;
    }

    switch (xdp_act) {
    diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
    index cffbf27c4656b..d516b28815af4 100644
    --- a/drivers/net/ethernet/freescale/enetc/enetc.c
    +++ b/drivers/net/ethernet/freescale/enetc/enetc.c
    @@ -1578,6 +1578,7 @@ static int enetc_clean_rx_ring_xdp(struct enetc_bdr *rx_ring,
    rx_byte_cnt += VLAN_HLEN;
    rx_byte_cnt += xdp_get_buff_len(&xdp_buff);

    + guard(local_lock_nested_bh)(&bpf_run_lock.redirect_lock);
    xdp_act = bpf_prog_run_xdp(prog, &xdp_buff);

    switch (xdp_act) {
    diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
    index c3b7694a74851..335b1e307d468 100644
    --- a/drivers/net/ethernet/freescale/fec_main.c
    +++ b/drivers/net/ethernet/freescale/fec_main.c
    @@ -1587,6 +1587,7 @@ fec_enet_run_xdp(struct fec_enet_private *fep, struct bpf_prog *prog,
    int err;
    u32 act;

    + guard(local_lock_nested_bh)(&bpf_run_lock.redirect_lock);
    act = bpf_prog_run_xdp(prog, xdp);

    /* Due xdp_adjust_tail and xdp_adjust_head: DMA sync for_device cover
    --
    2.43.0

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