Re: [Intel-wired-lan] [PATCH iwl-next v3 2/5] libeth: handle creating pools with unreadable buffers

[Alexander Lobakin <aleksander.lobakin@intel.com>]

From: Tantilov, Emil S <emil.s.tantilov@intel.com>
Date: Thu, 5 Mar 2026 14:04:52 -0800

> 
> 
> On 2/24/2026 9:46 AM, Alexander Lobakin wrote:
>> libeth uses netmems for quite some time already, so in order to
>> support unreadable frags / memory providers, it only needs to set
>> PP_FLAG_ALLOW_UNREADABLE_NETMEM when needed.
>> Also add a couple sanity checks to make sure the driver didn't mess
>> up the configuration options and, in case when an MP is installed,
>> return the truesize always equal to PAGE_SIZE, so that
>> libeth_rx_alloc() will never try to allocate frags. Memory providers
>> manage buffers on their own and expect 1:1 buffer / HW Rx descriptor
>> association.
>>
>> Bonus: mention in the libeth_sqe_type description that
>> LIBETH_SQE_EMPTY should also be used for netmem Tx SQEs -- they
>> don't need DMA unmapping.
>>
>> Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
>> Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
>> Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
>> ---
>>   include/net/libeth/tx.h                |  2 +-
>>   drivers/net/ethernet/intel/libeth/rx.c | 42 ++++++++++++++++++++++++++
>>   2 files changed, 43 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/net/libeth/tx.h b/include/net/libeth/tx.h
>> index c3db5c6f1641..a66fc2b3a114 100644
>> --- a/include/net/libeth/tx.h
>> +++ b/include/net/libeth/tx.h
>> @@ -12,7 +12,7 @@
>>     /**
>>    * enum libeth_sqe_type - type of &libeth_sqe to act on Tx completion
>> - * @LIBETH_SQE_EMPTY: unused/empty OR XDP_TX/XSk frame, no action
>> required
>> + * @LIBETH_SQE_EMPTY: empty OR netmem/XDP_TX/XSk frame, no action
>> required
>>    * @LIBETH_SQE_CTX: context descriptor with empty SQE, no action
>> required
>>    * @LIBETH_SQE_SLAB: kmalloc-allocated buffer, unmap and kfree()
>>    * @LIBETH_SQE_FRAG: mapped skb frag, only unmap DMA
>> diff --git a/drivers/net/ethernet/intel/libeth/rx.c b/drivers/net/
>> ethernet/intel/libeth/rx.c
>> index 8874b714cdcc..11e6e8f353ef 100644
>> --- a/drivers/net/ethernet/intel/libeth/rx.c
>> +++ b/drivers/net/ethernet/intel/libeth/rx.c
>> @@ -6,6 +6,7 @@
>>   #include <linux/export.h>
>>     #include <net/libeth/rx.h>
>> +#include <net/netdev_queues.h>
>>     /* Rx buffer management */
>>   @@ -139,9 +140,47 @@ static bool
>> libeth_rx_page_pool_params_zc(struct libeth_fq *fq,
>>       fq->buf_len = clamp(mtu, LIBETH_RX_BUF_STRIDE, max);
>>       fq->truesize = fq->buf_len;
>>   +    /*
>> +     * Allow frags only for kernel pages. `fq->truesize == pp->max_len`
>> +     * will always fall back to regular page_pool_alloc_netmems()
>> +     * regardless of the MTU / FQ buffer size.
>> +     */
>> +    if (pp->flags & PP_FLAG_ALLOW_UNREADABLE_NETMEM)
>> +        fq->truesize = pp->max_len;
>> +
>>       return true;
>>   }
>>   +/**
>> + * libeth_rx_page_pool_check_unread - check input params for
>> unreadable MPs
>> + * @fq: buffer queue to check
>> + * @pp: &page_pool_params for the queue
>> + *
>> + * Make sure we don't create an invalid pool with full-frame unreadable
>> + * buffers, bidirectional unreadable buffers or so, and configure the
>> + * ZC payload pool accordingly.
>> + *
>> + * Return: true on success, false on invalid input params.
>> + */
>> +static bool libeth_rx_page_pool_check_unread(const struct libeth_fq *fq,
>> +                         struct page_pool_params *pp)
>> +{
>> +    if (!netif_rxq_has_unreadable_mp(pp->netdev, pp->queue_idx))
>> +        return true;
> 
> This is causing a crash on IDPF:
> 
> [  420.570632] BUG: kernel NULL pointer dereference, address:
> 00000000000000e8
> [  420.570684] #PF: supervisor read access in kernel mode
> [  420.570712] #PF: error_code(0x0000) - not-present page
> [  420.570739] PGD 0
> [  420.570757] Oops: Oops: 0000 [#1] SMP NOPTI
> [  420.570784] CPU: 35 UID: 0 PID: 1058 Comm: kworker/u258:8 Kdump:
> loaded Tainted: G S         OE       7.0.0-rc1-next-devq-030526+ #34
> PREEMPT(full)
> [  420.570844] Tainted: [S]=CPU_OUT_OF_SPEC, [O]=OOT_MODULE,
> [E]=UNSIGNED_MODULE
> [  420.570872] Hardware name: Intel Corporation M50CYP2SBSTD/
> M50CYP2SBSTD, BIOS SE5C6200.86B.0027.P10.2201070222 01/07/2022
> [  420.570912] Workqueue: idpf-0000:83:00.0-vc_event idpf_vc_event_task
> [idpf]
> [  420.570967] RIP: 0010:netif_rxq_has_unreadable_mp+0xf/0x30
> [  420.571004] Code: 2e 0f 1f 84 00 00 00 00 00 66 90 90 90 90 90 90 90
> 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 0f 1f 44 00 00 89 f6 48 c1 e6
> 08 <48> 03 b7 e8 00 00 00 48 83 be c8 00 00 00 00 0f 95 c0 e9 8a 25 2b
> [  420.571078] RSP: 0018:ff6bf03aa83e7bd8 EFLAGS: 00010246
> [  420.571109] RAX: ff3579f9888ed0d0 RBX: ff6bf03aa83e7c78 RCX:
> 0000000000000000
> [  420.571145] RDX: 0000000000000000 RSI: 0000000000000000 RDI:
> 0000000000000000
> [  420.571178] RBP: ff6bf03aa83e7be0 R08: 0000000000000040 R09:
> 000000004b1a4093
> [  420.571213] R10: 0000000000000003 R11: ff3579f9bed90ee0 R12:
> ff3579f9d58c6060
> [  420.571247] R13: ff6bf03aa83e7d88 R14: 0000000000000001 R15:
> ff3579f9d58c6050
> [  420.571281] FS:  0000000000000000(0000) GS:ff357a195e9db000(0000)
> knlGS:0000000000000000
> [  420.571320] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  420.571350] CR2: 00000000000000e8 CR3: 00000023b2e2a006 CR4:
> 0000000000773ef0
> [  420.571384] PKRU: 55555554
> [  420.571402] Call Trace:
> [  420.571419]  <TASK>
> [  420.571436]  libeth_rx_fq_create+0x7c/0x380 [libeth]
> [  420.571479]  libie_ctlq_init+0x304/0x460 [libie_cp]
> [  420.571516]  libie_ctlq_xn_init+0x29/0x230 [libie_cp]
> [  420.571550]  idpf_init_dflt_mbx+0xa7/0x170 [idpf]
> [  420.571611]  idpf_vc_event_task+0x15d/0x2f0 [idpf]
> [  420.571655]  process_one_work+0x226/0x730
> [  420.571699]  worker_thread+0x19e/0x340
> [  420.571729]  ? __pfx_worker_thread+0x10/0x10
> [  420.571760]  kthread+0xf4/0x130
> [  420.571785]  ? __pfx_kthread+0x10/0x10
> [  420.571813]  ret_from_fork+0x32c/0x410
> [  420.571844]  ? __pfx_kthread+0x10/0x10
> [  420.571871]  ret_from_fork_asm+0x1a/0x30
> [  420.571909]  </TASK>
> 
> The driver will call idpf_init_dflt_mbx() before the netdevs are created.
> 
> Thanks,
> Emil

This series is based on top of the latest net-next as the PR will be
sent soon. net-next doesn't have libie_ctql.

For the tree which contains ixd this will look different as it
introduces ability to pass a device instead of napi_struct. Once this PR
is accepted, we'll rebase the next-queue to handle this.

Thanks,
Olek