RE: [Intel-wired-lan] [PATCH net v2 1/1] i40e: xsk: advance next_to_clean on status descriptors

Loktionov, Aleksandr
2025-10-22T06:41:12Z

> -----Original Message-----
> From: Intel-wired-lan <intel-wired-lan-bounces@osuosl.org> On Behalf
> Of Alessandro Decina
> Sent: Tuesday, October 21, 2025 7:32 PM
> To: netdev@vger.kernel.org
> Cc: Fijalkowski, Maciej <maciej.fijalkowski@intel.com>; David S.
> Miller <davem@davemloft.net>; Alexei Starovoitov <ast@kernel.org>;
> Andrew Lunn <andrew+netdev@lunn.ch>; Daniel Borkmann
> <daniel@iogearbox.net>; Eric Dumazet <edumazet@google.com>; Jakub
> Kicinski <kuba@kernel.org>; Jesper Dangaard Brouer <hawk@kernel.org>;
> John Fastabend <john.fastabend@gmail.com>; Paolo Abeni
> <pabeni@redhat.com>; Kitszel, Przemyslaw
> <przemyslaw.kitszel@intel.com>; Stanislav Fomichev <sdf@fomichev.me>;
> Sarkar, Tirthendu <tirthendu.sarkar@intel.com>; Nguyen, Anthony L
> <anthony.l.nguyen@intel.com>; bpf@vger.kernel.org; intel-wired-
> lan@lists.osuosl.org; linux-kernel@vger.kernel.org; Alessandro Decina
> <alessandro.d@gmail.com>
> Subject: [Intel-wired-lan] [PATCH net v2 1/1] i40e: xsk: advance
> next_to_clean on status descriptors
>
> Whenever a status descriptor is received, i40e processes and skips
> over it, correctly updating next_to_process but forgetting to update
> next_to_clean. In the next iteration this accidentally causes the
> creation of an invalid multi-buffer xdp_buff where the first fragment
> is the status descriptor.
>
> If then a skb is constructed from such an invalid buffer - because the
> eBPF program returns XDP_PASS - a panic occurs:
>
> [ 5866.367317] BUG: unable to handle page fault for address:
> ffd31c37eab1c980 [ 5866.375050] #PF: supervisor read access in kernel
> mode [ 5866.380825] #PF: error_code(0x0000) - not-present page [
> 5866.386602] PGD 0 [ 5866.388867] Oops: Oops: 0000 [#1] SMP NOPTI [
> 5866.393575] CPU: 34 UID: 0 PID: 0 Comm: swapper/34 Not tainted
> 6.17.0-custom #1 PREEMPT(voluntary) [ 5866.403740] Hardware name:
> Supermicro AS -2115GT-HNTR/H13SST-G, BIOS 3.2 03/20/2025 [
> 5866.412339] RIP: 0010:memcpy+0x8/0x10 [ 5866.416454] Code: cc cc 90
> cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc 90 90 90 90 90 90 90 90
> 90 90 90 90 90 90 90 90 66 90 48 89 f8 48 89 d1 <f3> a4 e9 fc 26 c0 fe
> 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 [ 5866.437538] RSP:
> 0018:ff428d9ec0bb0ca8 EFLAGS: 00010286 [ 5866.443415] RAX:
> ff2dd26dbd8f0000 RBX: ff2dd265ad161400 RCX: 00000000000004e1 [
> 5866.451435] RDX: 00000000000004e1 RSI: ffd31c37eab1c980 RDI:
> ff2dd26dbd8f0000 [ 5866.459454] RBP: ff428d9ec0bb0d40 R08:
> 0000000000000000 R09: 0000000000000000 [ 5866.467470] R10:
> 0000000000000000 R11: 0000000000000000 R12: ff428d9eec726ef8 [
> 5866.475490] R13: ff2dd26dbd8f0000 R14: ff2dd265ca2f9fc0 R15:
> ff2dd26548548b80 [ 5866.483509] FS: 0000000000000000(0000)
> GS:ff2dd2c363592000(0000) knlGS:0000000000000000 [ 5866.492600] CS:
> 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 5866.499060] CR2:
> ffd31c37eab1c980 CR3: 0000000178d7b040 CR4: 0000000000f71ef0 [
> 5866.507079] PKRU: 55555554 [ 5866.510125] Call Trace:
> [ 5866.512867] <IRQ>
> [ 5866.515132] ? i40e_clean_rx_irq_zc+0xc50/0xe60 [i40e] [
> 5866.520921] i40e_napi_poll+0x2d8/0x1890 [i40e] [ 5866.526022] ?
> srso_alias_return_thunk+0x5/0xfbef5
> [ 5866.531408] ? raise_softirq+0x24/0x70 [ 5866.535623] ?
> srso_alias_return_thunk+0x5/0xfbef5
> [ 5866.541011] ? srso_alias_return_thunk+0x5/0xfbef5
> [ 5866.546397] ? rcu_sched_clock_irq+0x225/0x1800 [ 5866.551493]
> __napi_poll+0x30/0x230 [ 5866.555423] net_rx_action+0x20b/0x3f0 [
> 5866.559643] handle_softirqs+0xe4/0x340 [ 5866.563962]
> __irq_exit_rcu+0x10e/0x130 [ 5866.568283] irq_exit_rcu+0xe/0x20 [
> 5866.572110] common_interrupt+0xb6/0xe0 [ 5866.576425] </IRQ> [
> 5866.578791] <TASK>
>
> Advance next_to_clean to ensure invalid xdp_buff(s) aren't created.
>
> Fixes: 1c9ba9c14658 ("i40e: xsk: add RX multi-buffer support")
> Signed-off-by: Alessandro Decina <alessandro.d@gmail.com>
> ---
> drivers/net/ethernet/intel/i40e/i40e_xsk.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> index 9f47388eaba5..dbc19083bbb7 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> @@ -441,13 +441,18 @@ int i40e_clean_rx_irq_zc(struct i40e_ring
> *rx_ring, int budget)
> dma_rmb();
>
> if (i40e_rx_is_programming_status(qword)) {
> + u16 ntp;
> +
> i40e_clean_programming_status(rx_ring,
> rx_desc->raw.qword[0],
> qword);
> bi = *i40e_rx_bi(rx_ring, next_to_process);
> xsk_buff_free(bi);
> - if (++next_to_process == count)
> + ntp = next_to_process++;
> + if (next_to_process == count)
> next_to_process = 0;
> + if (next_to_clean == ntp)
> + next_to_clean = next_to_process;
> continue;
> }
>
> --
> 2.43.0

Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>