Message-ID: <IA3PR11MB89867864D4ED892C677CA8CEE5D6A@IA3PR11MB8986.namprd11.prod.outlook.com>
Date: Tue, 18 Nov 2025 12:13:33 +0000
From: "Loktionov, Aleksandr" <aleksandr.loktionov@...el.com>
To: Alessandro Decina <alessandro.d@...il.com>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>
CC: "Fijalkowski, Maciej" <maciej.fijalkowski@...el.com>, "David S. Miller"
	<davem@...emloft.net>, Alexei Starovoitov <ast@...nel.org>, Andrew Lunn
	<andrew+netdev@...n.ch>, Daniel Borkmann <daniel@...earbox.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, "Jesper Dangaard
 Brouer" <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>, "Paolo
 Abeni" <pabeni@...hat.com>, "Kitszel, Przemyslaw"
	<przemyslaw.kitszel@...el.com>, Stanislav Fomichev <sdf@...ichev.me>,
	"Sarkar, Tirthendu" <tirthendu.sarkar@...el.com>, "Nguyen, Anthony L"
	<anthony.l.nguyen@...el.com>, "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
	"intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [Intel-wired-lan] [PATCH net v4 1/1] i40e: xsk: advance
 next_to_clean on status descriptors



> -----Original Message-----
> From: Intel-wired-lan <intel-wired-lan-bounces@...osl.org> On Behalf
> Of Alessandro Decina
> Sent: Tuesday, November 18, 2025 12:31 PM
> To: netdev@...r.kernel.org
> Cc: Fijalkowski, Maciej <maciej.fijalkowski@...el.com>; David S.
> Miller <davem@...emloft.net>; Alexei Starovoitov <ast@...nel.org>;
> Andrew Lunn <andrew+netdev@...n.ch>; Daniel Borkmann
> <daniel@...earbox.net>; Eric Dumazet <edumazet@...gle.com>; Jakub
> Kicinski <kuba@...nel.org>; Jesper Dangaard Brouer <hawk@...nel.org>;
> John Fastabend <john.fastabend@...il.com>; Paolo Abeni
> <pabeni@...hat.com>; Kitszel, Przemyslaw
> <przemyslaw.kitszel@...el.com>; Stanislav Fomichev <sdf@...ichev.me>;
> Sarkar, Tirthendu <tirthendu.sarkar@...el.com>; Nguyen, Anthony L
> <anthony.l.nguyen@...el.com>; bpf@...r.kernel.org; intel-wired-
> lan@...ts.osuosl.org; linux-kernel@...r.kernel.org; Alessandro Decina
> <alessandro.d@...il.com>
> Subject: [Intel-wired-lan] [PATCH net v4 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>
> 
Commit message lacks test description.
Please add how you validated the fix (kernel version, NIC model, reproducer steps).

> Advance next_to_clean to ensure invalid xdp_buff(s) aren't created.
> 
> Move the common logic to i40e_clean_programming_status and update both
> i40e_clean_rx_irq and i40e_clean_rx_irq_zc accordingly.
> 
> Fixes: 1c9ba9c14658 ("i40e: xsk: add RX multi-buffer support")
> Signed-off-by: Alessandro Decina <alessandro.d@...il.com>
> ---
>  drivers/net/ethernet/intel/i40e/i40e_txrx.c   | 59 +++++++++++-------
> -
>  .../ethernet/intel/i40e/i40e_txrx_common.h    |  5 +-
>  drivers/net/ethernet/intel/i40e/i40e_xsk.c    | 14 ++---
>  3 files changed, 42 insertions(+), 36 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> index cc0b9efc2637..fe2190f4b9bc 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> @@ -1386,22 +1386,36 @@ static void i40e_reuse_rx_page(struct
> i40e_ring *rx_ring,
>   * @rx_ring: the rx ring that has this descriptor
>   * @qword0_raw: qword0
>   * @qword1: qword1 representing status_error_len in CPU ordering
> + * @next_to_process: pointer to next_to_process index
> + * @next_to_clean: pointer to next_to_clean index
>   *
>   * Flow director should handle FD_FILTER_STATUS to check its filter
> programming
>   * status being successful or not and take actions accordingly. FCoE
> should
>   * handle its context/filter programming/invalidation status and take
> actions.
>   *
> - * Returns an i40e_rx_buffer to reuse if the cleanup occurred,
> otherwise NULL.
> + * Returns false if what is passed is not a status descriptor.
>   **/
Please use kdoc Return: tag.
Kernel-doc is incomplete, please also document what 'true' means (status descriptor processed).

> -void i40e_clean_programming_status(struct i40e_ring *rx_ring, u64
> qword0_raw,
> -				   u64 qword1)
> +bool i40e_clean_programming_status(struct i40e_ring *rx_ring, u64
> qword0_raw,
> +				   u64 qword1, u16 *next_to_process,
> +				   u16 *next_to_clean)
>  {
> +	u16 ntp = *next_to_process;
>  	u8 id;
> 
> +	if (!i40e_rx_is_programming_status(qword1))
> +		return false;
> +
>  	id = FIELD_GET(I40E_RX_PROG_STATUS_DESC_QW1_PROGID_MASK,
> qword1);
> 
>  	if (id == I40E_RX_PROG_STATUS_DESC_FD_FILTER_STATUS)
>  		i40e_fd_handle_status(rx_ring, qword0_raw, qword1, id);
> +
> +	if (++*next_to_process == rx_ring->count)
> +		*next_to_process = 0;
Consider using u16_inc_wrap() instead of manual wrap.

> +	if (ntp == *next_to_clean)
> +		*next_to_clean = *next_to_process;
> +
> +	return true;
>  }
> 
>  /**
> @@ -1971,19 +1985,18 @@ static void i40e_rx_buffer_flip(struct
> i40e_rx_buffer *rx_buffer,  }
> 
>  /**
> - * i40e_get_rx_buffer - Fetch Rx buffer and synchronize data for use
> + * i40e_prepare_rx_buffer - Synchronize the buffer for use by the CPU
>   * @rx_ring: rx descriptor ring to transact packets on
> + * @rx_buffer: the rx buffer
>   * @size: size of buffer to add to skb
>   *
> - * This function will pull an Rx buffer from the ring and synchronize
> it
> - * for use by the CPU.
> + * This function will synchronize the given buffer for use by the
> CPU.
>   */
> -static struct i40e_rx_buffer *i40e_get_rx_buffer(struct i40e_ring
> *rx_ring,
> -						 const unsigned int size)
> +static struct i40e_rx_buffer *
> +i40e_prepare_rx_buffer(struct i40e_ring *rx_ring,
> +		       struct i40e_rx_buffer *rx_buffer,
> +		       const unsigned int size)
>  {
> -	struct i40e_rx_buffer *rx_buffer;
> -
> -	rx_buffer = i40e_rx_bi(rx_ring, rx_ring->next_to_process);
>  	rx_buffer->page_count =
>  #if (PAGE_SIZE < 8192)
>  		page_count(rx_buffer->page);
> @@ -2450,6 +2463,7 @@ static int i40e_clean_rx_irq(struct i40e_ring
> *rx_ring, int budget,
> 
>  	while (likely(total_rx_packets < (unsigned int)budget)) {
>  		u16 ntp = rx_ring->next_to_process;
> +		u16 ntc = rx_ring->next_to_clean;
>  		struct i40e_rx_buffer *rx_buffer;
>  		union i40e_rx_desc *rx_desc;
>  		struct sk_buff *skb;
> @@ -2480,21 +2494,15 @@ static int i40e_clean_rx_irq(struct i40e_ring
> *rx_ring, int budget,
>  		 */
>  		dma_rmb();
> 
> -		if (i40e_rx_is_programming_status(qword)) {
> -			i40e_clean_programming_status(rx_ring,
> -						      rx_desc->raw.qword[0],
> -						      qword);
> -			rx_buffer = i40e_rx_bi(rx_ring, ntp);
> -			i40e_inc_ntp(rx_ring);
> +		rx_buffer = i40e_rx_bi(rx_ring, ntp);
> +
> +		if (i40e_clean_programming_status(rx_ring,
> +						  rx_desc->raw.qword[0],
> qword,
> +						  &rx_ring->next_to_process,
> +						  &rx_ring->next_to_clean)) {
Wrap the call to i40e_clean_programming_status to stay within 80 columns.

>  			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;
> +			if (ntc != rx_ring->next_to_clean)
>  				cleaned_count++;
> -			}
>  			continue;
>  		}
> 
> @@ -2503,8 +2511,7 @@ static int i40e_clean_rx_irq(struct i40e_ring
> *rx_ring, int budget,
>  			break;
> 
>  		i40e_trace(clean_rx_irq, rx_ring, rx_desc, xdp);
> -		/* retrieve a buffer from the ring */
> -		rx_buffer = i40e_get_rx_buffer(rx_ring, size);
> +		i40e_prepare_rx_buffer(rx_ring, rx_buffer, size);
> 
>  		neop = i40e_is_non_eop(rx_ring, rx_desc);
>  		i40e_inc_ntp(rx_ring);
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx_common.h
> b/drivers/net/ethernet/intel/i40e/i40e_txrx_common.h
> index e26807fd2123..21d9ed878bf0 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_txrx_common.h
> +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx_common.h
> @@ -7,8 +7,9 @@
>  #include "i40e.h"
> 
>  int i40e_xmit_xdp_tx_ring(struct xdp_buff *xdp, struct i40e_ring
> *xdp_ring); -void i40e_clean_programming_status(struct i40e_ring
> *rx_ring, u64 qword0_raw,
> -				   u64 qword1);
> +bool i40e_clean_programming_status(struct i40e_ring *rx_ring, u64
> qword0_raw,
> +				   u64 qword1, u16 *next_to_clean,
> +				   u16 *next_to_process);
Argument order differs between header and implementation (next_to_clean vs next_to_process).
This will compile but is misleading and dangerous for future maintenance.
Please fix argument order to match.

>  void i40e_process_skb_fields(struct i40e_ring *rx_ring,
>  			     union i40e_rx_desc *rx_desc, struct sk_buff
> *skb);  void i40e_xdp_ring_update_tail(struct i40e_ring *xdp_ring);
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> index 9f47388eaba5..f8accc266c2c 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> @@ -440,14 +440,13 @@ int i40e_clean_rx_irq_zc(struct i40e_ring
> *rx_ring, int budget)
>  		 */
>  		dma_rmb();
> 
> -		if (i40e_rx_is_programming_status(qword)) {
> -			i40e_clean_programming_status(rx_ring,
> -						      rx_desc->raw.qword[0],
> -						      qword);
> -			bi = *i40e_rx_bi(rx_ring, next_to_process);
> +		bi = *i40e_rx_bi(rx_ring, next_to_process);
> +
> +		if (i40e_clean_programming_status(rx_ring,
> +						  rx_desc->raw.qword[0],
> +						  qword, &next_to_process,
> +						  &next_to_clean)) {
>  			xsk_buff_free(bi);
> -			if (++next_to_process == count)
> -				next_to_process = 0;
>  			continue;
>  		}
> 
> @@ -455,7 +454,6 @@ int i40e_clean_rx_irq_zc(struct i40e_ring
> *rx_ring, int budget)
>  		if (!size)
>  			break;
> 
> -		bi = *i40e_rx_bi(rx_ring, next_to_process);
>  		xsk_buff_set_size(bi, size);
>  		xsk_buff_dma_sync_for_cpu(bi);
> 
> --
> 2.43.0

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