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    Subject[PATCH net-next 19/24] net: fungible, gve, mtk, microchip, mana: 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: "K. Y. Srinivasan" <kys@microsoft.com>
    Cc: Alexei Starovoitov <ast@kernel.org>
    Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
    Cc: Dexuan Cui <decui@microsoft.com>
    Cc: Dimitris Michailidis <dmichail@fungible.com>
    Cc: Felix Fietkau <nbd@nbd.name>
    Cc: Haiyang Zhang <haiyangz@microsoft.com>
    Cc: Horatiu Vultur <horatiu.vultur@microchip.com>
    Cc: Jeroen de Borst <jeroendb@google.com>
    Cc: Jesper Dangaard Brouer <hawk@kernel.org>
    Cc: John Crispin <john@phrozen.org>
    Cc: John Fastabend <john.fastabend@gmail.com>
    Cc: Lorenzo Bianconi <lorenzo@kernel.org>
    Cc: Mark Lee <Mark-MC.Lee@mediatek.com>
    Cc: Matthias Brugger <matthias.bgg@gmail.com>
    Cc: Praveen Kaligineedi <pkaligineedi@google.com>
    Cc: Sean Wang <sean.wang@mediatek.com>
    Cc: Shailend Chand <shailend@google.com>
    Cc: UNGLinuxDriver@microchip.com
    Cc: Wei Liu <wei.liu@kernel.org>
    Cc: bpf@vger.kernel.org
    Cc: linux-hyperv@vger.kernel.org
    Cc: linux-mediatek@lists.infradead.org
    Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    ---
    drivers/net/ethernet/fungible/funeth/funeth_rx.c | 1 +
    drivers/net/ethernet/google/gve/gve_rx.c | 12 +++++++-----
    drivers/net/ethernet/mediatek/mtk_eth_soc.c | 1 +
    drivers/net/ethernet/microchip/lan966x/lan966x_xdp.c | 1 +
    drivers/net/ethernet/microsoft/mana/mana_bpf.c | 1 +
    5 files changed, 11 insertions(+), 5 deletions(-)

    diff --git a/drivers/net/ethernet/fungible/funeth/funeth_rx.c b/drivers/net/ethernet/fungible/funeth/funeth_rx.c
    index 7e2584895de39..e7b1382545908 100644
    --- a/drivers/net/ethernet/fungible/funeth/funeth_rx.c
    +++ b/drivers/net/ethernet/fungible/funeth/funeth_rx.c
    @@ -152,6 +152,7 @@ static void *fun_run_xdp(struct funeth_rxq *q, skb_frag_t *frags, void *buf_va,
    xdp_prepare_buff(&xdp, buf_va, FUN_XDP_HEADROOM, skb_frag_size(frags) -
    (FUN_RX_TAILROOM + FUN_XDP_HEADROOM), false);

    + guard(local_lock_nested_bh)(&bpf_run_lock.redirect_lock);
    xdp_prog = READ_ONCE(q->xdp_prog);
    act = bpf_prog_run_xdp(xdp_prog, &xdp);

    diff --git a/drivers/net/ethernet/google/gve/gve_rx.c b/drivers/net/ethernet/google/gve/gve_rx.c
    index 73655347902d2..504c8ef761a33 100644
    --- a/drivers/net/ethernet/google/gve/gve_rx.c
    +++ b/drivers/net/ethernet/google/gve/gve_rx.c
    @@ -779,11 +779,13 @@ static void gve_rx(struct gve_rx_ring *rx, netdev_features_t feat,
    page_info->page_offset, GVE_RX_PAD,
    len, false);
    old_data = xdp.data;
    - xdp_act = bpf_prog_run_xdp(xprog, &xdp);
    - if (xdp_act != XDP_PASS) {
    - gve_xdp_done(priv, rx, &xdp, xprog, xdp_act);
    - ctx->total_size += frag_size;
    - goto finish_ok_pkt;
    + scoped_guard(local_lock_nested_bh, &bpf_run_lock.redirect_lock) {
    + xdp_act = bpf_prog_run_xdp(xprog, &xdp);
    + if (xdp_act != XDP_PASS) {
    + gve_xdp_done(priv, rx, &xdp, xprog, xdp_act);
    + ctx->total_size += frag_size;
    + goto finish_ok_pkt;
    + }
    }

    page_info->pad += xdp.data - old_data;
    diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
    index 3cf6589cfdacf..477a74ee18c0a 100644
    --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
    +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
    @@ -1946,6 +1946,7 @@ static u32 mtk_xdp_run(struct mtk_eth *eth, struct mtk_rx_ring *ring,
    if (!prog)
    goto out;

    + guard(local_lock_nested_bh)(&bpf_run_lock.redirect_lock);
    act = bpf_prog_run_xdp(prog, xdp);
    switch (act) {
    case XDP_PASS:
    diff --git a/drivers/net/ethernet/microchip/lan966x/lan966x_xdp.c b/drivers/net/ethernet/microchip/lan966x/lan966x_xdp.c
    index 9ee61db8690b4..026311af07f9e 100644
    --- a/drivers/net/ethernet/microchip/lan966x/lan966x_xdp.c
    +++ b/drivers/net/ethernet/microchip/lan966x/lan966x_xdp.c
    @@ -84,6 +84,7 @@ int lan966x_xdp_run(struct lan966x_port *port, struct page *page, u32 data_len)
    xdp_prepare_buff(&xdp, page_address(page),
    IFH_LEN_BYTES + XDP_PACKET_HEADROOM,
    data_len - IFH_LEN_BYTES, false);
    + guard(local_lock_nested_bh)(&bpf_run_lock.redirect_lock);
    act = bpf_prog_run_xdp(xdp_prog, &xdp);
    switch (act) {
    case XDP_PASS:
    diff --git a/drivers/net/ethernet/microsoft/mana/mana_bpf.c b/drivers/net/ethernet/microsoft/mana/mana_bpf.c
    index 23b1521c0df96..d465b1dd9fca0 100644
    --- a/drivers/net/ethernet/microsoft/mana/mana_bpf.c
    +++ b/drivers/net/ethernet/microsoft/mana/mana_bpf.c
    @@ -93,6 +93,7 @@ u32 mana_run_xdp(struct net_device *ndev, struct mana_rxq *rxq,
    xdp_init_buff(xdp, PAGE_SIZE, &rxq->xdp_rxq);
    xdp_prepare_buff(xdp, buf_va, XDP_PACKET_HEADROOM, pkt_len, false);

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

    rx_stats = &rxq->stats;
    --
    2.43.0

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