linux-kernel - Re: [PATCH v2 net-next 0/2] virtio_net: add page

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Message-ID: <38412fe3-76e2-47df-91d6-4815982742ff@meta.com>
Date: Wed, 28 Jan 2026 21:45:34 -0800
From: Vishwanath Seshagiri <vishs@...a.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: "Michael S . Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        Eugenio Pérez
 <eperezma@...hat.com>,
        Andrew Lunn <andrew+netdev@...n.ch>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet
 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
        David Wei <dw@...idwei.uk>, netdev@...r.kernel.org,
        virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 net-next 0/2] virtio_net: add page_pool support

On 1/28/26 5:37 PM, Jakub Kicinski wrote:
> On Wed, 28 Jan 2026 13:20:29 -0800 Vishwanath Seshagiri wrote:
>> Introduce page_pool support in virtio_net driver to enable page recycling
>> in RX buffer allocation and avoid repeated page allocator calls. This
>> applies to mergeable and small buffer modes.
>>
>> Beyond performance improvements, this patch is a prerequisite for enabling
>> memory provider-based zero-copy features in virtio_net, specifically devmem
>> TCP and io_uring ZCRX, which require drivers to use page_pool for buffer
>> management.
> 
> Struggles to boot in the CI:
> 
> [   11.424197][    C0] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN
> [   11.424454][    C0] KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> [   11.424606][    C0] CPU: 0 UID: 0 PID: 271 Comm: ip Not tainted 6.19.0-rc6-virtme #1 PREEMPT(full)
> [   11.424784][    C0] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
> [   11.424913][    C0] RIP: 0010:page_pool_alloc_frag_netmem+0x34/0x8e0
> [   11.425054][    C0] Code: b8 00 00 00 00 00 fc ff df 41 57 41 89 c8 41 56 41 55 41 89 d5 48 89 fa 41 54 48 c1 ea 03 49 89 f4 55 53 48 89 fb 48 83 ec 30 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e 32 05 00 00 8b 0b 83 f9 3f 0f
> [   11.425413][    C0] RSP: 0018:ffa0000000007a00 EFLAGS: 00010286
> [   11.425544][    C0] RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000820
> [   11.425697][    C0] RDX: 0000000000000000 RSI: ffa0000000007ac0 RDI: 0000000000000000
> [   11.425846][    C0] RBP: 1ff4000000000f54 R08: 0000000000000820 R09: fff3fc0000000f8f
> [   11.426000][    C0] R10: fff3fc0000000f90 R11: 0000000000000001 R12: ffa0000000007ac0
> [   11.426156][    C0] R13: 0000000000000600 R14: ff11000008719d00 R15: ff1100000926de00
> [   11.426308][    C0] FS:  00007f4db5334400(0000) GS:ff110000786fe000(0000) knlGS:0000000000000000
> [   11.426487][    C0] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   11.426617][    C0] CR2: 00000000004e5e60 CR3: 000000000b9da001 CR4: 0000000000771ef0
> [   11.426768][    C0] PKRU: 55555554
> [   11.426846][    C0] Call Trace:
> [   11.426927][    C0]  <IRQ>
> [   11.426981][    C0]  ? alloc_chain_hlocks+0x1e5/0x5c0
> [   11.427085][    C0]  ? buf_to_xdp.isra.0+0x2f0/0x2f0
> [   11.427190][    C0]  page_pool_alloc_frag+0xe/0x20
> [   11.427289][    C0]  add_recvbuf_mergeable+0x1e0/0x940
> [   11.427392][    C0]  ? page_to_skb+0x760/0x760
> [   11.427497][    C0]  ? lock_acquire.part.0+0xbc/0x260
> [   11.427597][    C0]  ? find_held_lock+0x2b/0x80
> [   11.427696][    C0]  try_fill_recv+0x180/0x240
> [   11.427794][    C0]  virtnet_poll+0xc79/0x1450
> [   11.427901][    C0]  ? receive_buf+0x690/0x690
> [   11.428005][    C0]  ? virtnet_xdp_handler+0x900/0x900
> [   11.428109][    C0]  ? do_raw_spin_unlock+0x59/0x250
> [   11.428208][    C0]  ? rcu_is_watching+0x15/0xd0
> [   11.428310][    C0]  __napi_poll.constprop.0+0x97/0x390
> [   11.428415][    C0]  net_rx_action+0x4f6/0xed0
> [   11.428517][    C0]  ? run_backlog_napi+0x90/0x90
> [   11.428617][    C0]  ? sched_balance_domains+0x270/0xd40
> [   11.428721][    C0]  ? lockdep_hardirqs_on_prepare.part.0+0x9a/0x160
> [   11.428844][    C0]  ? lockdep_hardirqs_on+0x84/0x130
> [   11.428949][    C0]  ? sched_balance_update_blocked_averages+0x137/0x1a0
> [   11.429073][    C0]  ? mark_held_locks+0x40/0x70
> [   11.429172][    C0]  handle_softirqs+0x1d7/0x840
> [   11.429271][    C0]  ? _local_bh_enable+0xd0/0xd0
> [   11.429371][    C0]  ? __flush_smp_call_function_queue+0x449/0x6d0
> [   11.429497][    C0]  ? rcu_is_watching+0x15/0xd0
> [   11.429597][    C0]  do_softirq+0xa9/0xe0
> 
> https://urldefense.com/v3/__https://netdev-ctrl.bots.linux.dev/logs/vmksft/virtio/results/494081/1-basic-features-sh/stderr__;!!Bt8RZUm9aw!7wS5Fv2oMa1yF_50zUYFtTbdPGX3y338sThfMUM_j_v_r6DUE5bRwHw9N4yAEVYm-uYHa48$

The CI error is a bug in my patch where page pools is not created for
all queues when num_online_cpus < max_queue_pairs. This is the issue
Jason caught about using max_queue_pairs instead of curr_queue_pairs.
I will fix it in v3.