Subject: Re: [PATCH net-next] virtio_net: Increase RSS max key size to match NETDEV_RSS_KEY_LEN

From: Jakub Kicinski <[email-masked]>
Date: Thu, 22 Jan 2026 07:52:06 -0800

On Thu, 22 Jan 2026 14:45:27 +0530 Srujana Challa wrote:
> Increase VIRTIO_NET_RSS_MAX_KEY_SIZE from 40 to 52 bytes to align with
> the kernel's standard RSS key length defined by NETDEV_RSS_KEY_LEN.

I've been meaning to bump NETDEV_RSS_KEY_LEN to 128 or some such.
Most modern drivers can't use netdev_rss_key_fill() either because
core generates a tiny key. And the devices support hashing over two
layers of IPv6 for tunnels.

Willem, WDYT? Is there a reason to keep the core key small?
Or deprecate netdev_rss_key_fill()?

> The virtio specification requires devices to support at least 40 bytes
> for the RSS key size. However, devices may support larger key sizes
> up to 52 bytes (as reported by the device's rss_max_key_size config
> field). This change allows such devices to work properly.
> Previously, devices reporting rss_max_key_size > 40 would fail with
> an error during initialization.
> 
> The driver already handles variable key sizes dynamically through
> vi->rss_key_size, so increasing the maximum limit is safe and
> maintains backward compatibility with devices that support smaller
> key sizes.

> -#define VIRTIO_NET_RSS_MAX_KEY_SIZE     40
> +#define VIRTIO_NET_RSS_MAX_KEY_SIZE     52