Re: [PATCH net v2 1/8] xsk: reject sw-csum UMEM binding to IFF_TX_SKB_NO_LINEAR devices

[sashiko-bot@kernel.org]

Sashiko AI review found 1 potential issue(s):
- [High] The patch unconditionally rejects pool assignment for devices with IFF_TX_SKB_NO_LINEAR if tx_sw_csum is enabled, which incorrectly breaks native Zero-Copy (ZC) setups on those devices.
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commit 5beba1aaed8c200424f98af3c07472ab4da8d451
Author: Jason Xing <kerneljasonxing@gmail.com>

xsk: reject sw-csum UMEM binding to IFF_TX_SKB_NO_LINEAR devices

This commit rejects UMEM bindings for devices that advertise
IFF_TX_SKB_NO_LINEAR when software checksumming (tx_sw_csum) is enabled.
This prevents a warning and panic in skb_checksum_help() which relies on a
linear skb head.

Link: https://lore.kernel.org/all/20260419045822.843BFC2BCAF@smtp.kernel.org/#t

> diff --git a/net/xdp/xsk_buff_pool.c b/net/xdp/xsk_buff_pool.c
> index cd7bc50872f6b..d981cfdd85357 100644
> --- a/net/xdp/xsk_buff_pool.c
> +++ b/net/xdp/xsk_buff_pool.c
> @@ -175,6 +175,9 @@ int xp_assign_dev(struct xsk_buff_pool *pool,
>  	if (force_zc && force_copy)
>  		return -EINVAL;
>  
> +	if (pool->tx_sw_csum && (netdev->priv_flags & IFF_TX_SKB_NO_LINEAR))
> +		return -EOPNOTSUPP;
> +

Does this unconditionally reject the pool assignment even for native
Zero-Copy (ZC) setups?

In native XDP_ZEROCOPY mode, AF_XDP descriptors are sent directly to the
hardware. No sk_buff is allocated, so skb_checksum_help() is never called,
making the tx_sw_csum flag irrelevant and safe to ignore.

By placing this check before determining if native ZC is available, does
this break ZC mode on drivers like virtio_net for applications that pass
the XDP_UMEM_TX_SW_CSUM flag as a fallback?

Should this check be deferred until we are certain we are using generic
copy mode, such as when force_copy is true or after native ZC setup fails?

>  	if (xsk_get_pool_from_qid(netdev, queue_id))
>  		return -EBUSY;
>

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Sashiko AI review · https://sashiko.dev/#/patchset/20260420082805.14844-1-kerneljasonxing@gmail.com?part=1