RE: [Intel-wired-lan] [PATCH net v3 1/1] i40e: xsk: advance next_to_clean on status descriptors

Loktionov, Aleksandr
2025-11-14T05:50:19Z

> -----Original Message-----
> From: Intel-wired-lan <intel-wired-lan-bounces@osuosl.org> On Behalf
> Of Alessandro Decina
> Sent: Thursday, November 13, 2025 9:25 AM
> 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 v3 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.
>
> Rename i40e_inc_ntp to i40e_inc_ntp_ntc. Make it take an optional
> pointer to next_to_clean so it's harder for callers to accidentally
> forget to advance it.
>
> Fixes: 1c9ba9c14658 ("i40e: xsk: add RX multi-buffer support")
> Signed-off-by: Alessandro Decina <alessandro.d@gmail.com>
> ---
> drivers/net/ethernet/intel/i40e/i40e_txrx.c | 33 ++++++++++++------
> -
> .../ethernet/intel/i40e/i40e_txrx_common.h | 2 ++
> drivers/net/ethernet/intel/i40e/i40e_xsk.c | 17 ++++++----
> 3 files changed, 34 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> index cc0b9efc2637..d3dae895a058 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> @@ -2359,15 +2359,24 @@ void i40e_finalize_xdp_rx(struct i40e_ring
> *rx_ring, unsigned int xdp_res) }
>
> /**
> - * i40e_inc_ntp: Advance the next_to_process index
> + * i40e_inc_ntp_ntc: Advance the next_to_process and next_to_clean
> + indexes
> * @rx_ring: Rx ring
> + * @next_to_process: Pointer to next_to_process
> + * @next_to_clean: Pointer to next_to_clean or NULL
> + *
> + * This function advances the next_to_process index. If next_to_clean
> + is not
> + * NULL, it is advanced as well.
> **/
> -static void i40e_inc_ntp(struct i40e_ring *rx_ring)
> +void i40e_inc_ntp_ntc(struct i40e_ring *rx_ring, u16
> *next_to_process,
> + u16 *next_to_clean)
> {
> - u32 ntp = rx_ring->next_to_process + 1;
> + u16 ntp = *next_to_process + 1;
>
> ntp = (ntp < rx_ring->count) ? ntp : 0;
> - rx_ring->next_to_process = ntp;
> + *next_to_process = ntp;
> + if (next_to_clean)
> + *next_to_clean = ntp;
> +
> prefetch(I40E_RX_DESC(rx_ring, ntp));
> }
>
> @@ -2484,17 +2493,19 @@ static int i40e_clean_rx_irq(struct i40e_ring
> *rx_ring, int budget,
> i40e_clean_programming_status(rx_ring,
> rx_desc->raw.qword[0],
> qword);
> + bool eop;
> +
> rx_buffer = i40e_rx_bi(rx_ring, ntp);
> - i40e_inc_ntp(rx_ring);
> - i40e_reuse_rx_page(rx_ring, rx_buffer);
> /* Update ntc and bump cleaned count if not in
> the
> * middle of mb packet.
> */
> - if (rx_ring->next_to_clean == ntp) {
> - rx_ring->next_to_clean =
> - rx_ring->next_to_process;
> + eop = rx_ring->next_to_process ==
> + rx_ring->next_to_clean;
> + i40e_inc_ntp_ntc(rx_ring, &rx_ring-
> >next_to_process,
> + eop ? &rx_ring->next_to_clean :
> NULL);
> + if (eop)
> cleaned_count++;
> - }
> + i40e_reuse_rx_page(rx_ring, rx_buffer);
> continue;
> }
>
> @@ -2507,7 +2518,7 @@ static int i40e_clean_rx_irq(struct i40e_ring
> *rx_ring, int budget,
> rx_buffer = i40e_get_rx_buffer(rx_ring, size);
>
> neop = i40e_is_non_eop(rx_ring, rx_desc);
> - i40e_inc_ntp(rx_ring);
> + i40e_inc_ntp_ntc(rx_ring, &rx_ring->next_to_process,
> NULL);
>
> if (!xdp->data) {
> unsigned char *hard_start;
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx_common.h
> b/drivers/net/ethernet/intel/i40e/i40e_txrx_common.h
> index e26807fd2123..3d7e4b3404f0 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_txrx_common.h
> +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx_common.h
> @@ -17,6 +17,8 @@ void i40e_update_rx_stats(struct

...

> --
> 2.43.0

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