Subject: Re: [PATCH net-next 2/3] fbnic: Support larger zcrx receive buffers

From: Jakub Kicinski <[email-masked]>
Date: Fri, 22 May 2026 07:03:01 -0700

On Fri, 22 May 2026 13:32:21 +0200 Björn Töpel wrote:
> io_uring zcrx can provide receive buffers larger than PAGE_SIZE
> through QCFG_RX_PAGE_SIZE. Advertise the parameter and use the
> configured size when creating the PPQ page pool.
> 
> The NIC still consumes PPQ buffers as 4 KiB BDQ fragments. For larger
> zcrx buffers, allocate the page pool with the requested order and set
> the PPQ fragment shift from rx_page_size, so one net_iov can cover
> multiple hardware fragments.
> 
> The core validates the zcrx request and checks that the imported
> memory can be represented as rx_buf_len-sized DMA chunks. Fbnic still
> has to validate the rendered queue configuration against its own BDQ
> geometry: larger receive buffers consume multiple 4 KiB PPQ entries,
> and the PPQ must retain usable depth after that expansion.
> 
> Use the rendered per-queue rx_page_size on the normal open path as
> well. This preserves a memory-provider binding made while the netdev
> is down instead of falling back to the default PPQ geometry on open.

> +static u32 fbnic_qcfg_rx_page_size(const struct netdev_queue_config *qcfg)
> +{
> +	return qcfg->rx_page_size ?: PAGE_SIZE;

Isn't there a callback to set the defaults so that the driver doesn't
have to do this sort of stuff?

> +}
> +
> +static u32 fbnic_rx_page_frag_count(u32 rx_page_size)
> +{
> +	return rx_page_size / FBNIC_BD_FRAG_SIZE;
> +}
> +
> +static u8 fbnic_rx_page_frag_shift(u32 rx_page_size)
> +{
> +	return ilog2(fbnic_rx_page_frag_count(rx_page_size));
> +}
> +
> +static int fbnic_validate_rx_page_size(struct fbnic_net *fbn, u32 rx_page_size,
> +				       struct netlink_ext_ack *extack)
> +{
> +	u32 frag_count, ppq_bufs;
> +
> +	if (!is_power_of_2(rx_page_size)) {
> +		NL_SET_ERR_MSG_MOD(extack,
> +				   "rx_page_size must be a power of 2");
> +		return -EINVAL;
> +	}
> +
> +	if (rx_page_size < PAGE_SIZE) {

If the PAGE_SIZE == 64kB it should be fine to have smaller frags, no?
Or something breaks?

> +		NL_SET_ERR_MSG_MOD(extack,
> +				   "rx_page_size must be at least PAGE_SIZE");
> +		return -EINVAL;
> +	}
> +
> +	if (!IS_ALIGNED(rx_page_size, FBNIC_BD_FRAG_SIZE)) {
> +		NL_SET_ERR_MSG_MOD(extack,
> +				   "rx_page_size must be 4K aligned");

"multiple" is probably a better word than "aligned" for size params?

> +		return -EINVAL;
> +	}
> +
> +	frag_count = fbnic_rx_page_frag_count(rx_page_size);
> +	ppq_bufs = fbn->ppq_size / frag_count;
> +	/* The PPQ is sized in 4K hardware fragments, but the software ring
> +	 * has one entry per page-pool allocation. Keep at least two entries so
> +	 * empty/full ring accounting still leaves one postable buffer.
> +	 */
> +	if (ppq_bufs < 2) {
> +		NL_SET_ERR_MSG_MOD(extack,
> +				   "rx_page_size leaves too few PPQ buffers");

Maybe "rx-jumbo ring size too small for rx_page_size" ?

Core does revalidate the config on ring size changes, right?

> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
>  static int
>  fbnic_alloc_qt_page_pools(struct fbnic_net *fbn, struct fbnic_q_triad *qt,
> -			  unsigned int rxq_idx)
> +			  unsigned int rxq_idx, u32 rx_page_size)
>  {
>  	struct page_pool_params pp_params = {
>  		.order = 0,
> @@ -1596,6 +1649,8 @@ fbnic_alloc_qt_page_pools(struct fbnic_net *fbn, struct fbnic_q_triad *qt,
>  
>  	qt->sub0.page_pool = pp;
>  	if (netif_rxq_has_unreadable_mp(fbn->netdev, rxq_idx)) {
> +		pp_params.order = ilog2(rx_page_size) - PAGE_SHIFT;
> +		pp_params.max_len = rx_page_size;
>  		pp_params.flags |= PP_FLAG_ALLOW_UNREADABLE_NETMEM;
>  		pp_params.dma_dir = DMA_FROM_DEVICE;
>  
> @@ -2018,12 +2073,19 @@ static int fbnic_alloc_tx_qt_resources(struct fbnic_net *fbn,
>  
>  static int fbnic_alloc_rx_qt_resources(struct fbnic_net *fbn,
>  				       struct fbnic_napi_vector *nv,
> -				       struct fbnic_q_triad *qt)
> +				       struct fbnic_q_triad *qt,
> +				       u32 rx_page_size)
>  {
>  	struct device *dev = fbn->netdev->dev.parent;
>  	int err;
>  
> -	err = fbnic_alloc_qt_page_pools(fbn, qt, qt->cmpl.q_idx);
> +	err = fbnic_validate_rx_page_size(fbn, rx_page_size, NULL);
> +	if (err)
> +		return err;
> +
> +	qt->sub1.frag_shift = fbnic_rx_page_frag_shift(rx_page_size);
> +
> +	err = fbnic_alloc_qt_page_pools(fbn, qt, qt->cmpl.q_idx, rx_page_size);
>  	if (err)
>  		return err;
>  
> @@ -2087,7 +2149,13 @@ static int fbnic_alloc_nv_resources(struct fbnic_net *fbn,
>  
>  	/* Allocate Rx Resources */
>  	for (j = 0; j < nv->rxt_count; j++, i++) {
> -		err = fbnic_alloc_rx_qt_resources(fbn, nv, &nv->qt[i]);
> +		struct netdev_queue_config qcfg;
> +		u32 rx_page_size;
> +
> +		netdev_queue_config(fbn->netdev, nv->qt[i].cmpl.q_idx, &qcfg);
> +		rx_page_size = fbnic_qcfg_rx_page_size(&qcfg);
> +		err = fbnic_alloc_rx_qt_resources(fbn, nv, &nv->qt[i],
> +						  rx_page_size);
>  		if (err)
>  			goto free_qt_resources;
>  	}
> @@ -2852,9 +2920,16 @@ static int fbnic_queue_mem_alloc(struct net_device *dev,
>  	const struct fbnic_q_triad *real;
>  	struct fbnic_q_triad *qt = qmem;
>  	struct fbnic_napi_vector *nv;
> +	u32 rx_page_size = fbnic_qcfg_rx_page_size(qcfg);
> +	int err;
>  
> -	if (!netif_running(dev))
> -		return fbnic_alloc_qt_page_pools(fbn, qt, idx);
> +	if (!netif_running(dev)) {
> +		err = fbnic_validate_rx_page_size(fbn, rx_page_size, NULL);

Hm. Is the validate callback not called in case the device is down?

> +		if (err)
> +			return err;
> +
> +		return fbnic_alloc_qt_page_pools(fbn, qt, idx, rx_page_size);
> +	}
>  
>  	real = container_of(fbn->rx[idx], struct fbnic_q_triad, cmpl);
>  	nv = fbn->napi[idx % fbn->num_napi];
> @@ -2864,11 +2939,20 @@ static int fbnic_queue_mem_alloc(struct net_device *dev,
>  	qt->sub0.frag_shift = real->sub0.frag_shift;
>  	fbnic_ring_init(&qt->sub1, real->sub1.doorbell, real->sub1.q_idx,
>  			real->sub1.flags);
> -	qt->sub1.frag_shift = real->sub1.frag_shift;
>  	fbnic_ring_init(&qt->cmpl, real->cmpl.doorbell, real->cmpl.q_idx,
>  			real->cmpl.flags);
>  
> -	return fbnic_alloc_rx_qt_resources(fbn, nv, qt);
> +	return fbnic_alloc_rx_qt_resources(fbn, nv, qt, rx_page_size);
> +}
> +
> +static int fbnic_validate_qcfg(struct net_device *dev,
> +			       struct netdev_queue_config *qcfg,
> +			       struct netlink_ext_ack *extack)
> +{
> +	struct fbnic_net *fbn = netdev_priv(dev);
> +
> +	return fbnic_validate_rx_page_size(fbn, fbnic_qcfg_rx_page_size(qcfg),
> +					   extack);
>  }
>  
>  static void fbnic_queue_mem_free(struct net_device *dev, void *qmem)
> @@ -2970,4 +3054,6 @@ const struct netdev_queue_mgmt_ops fbnic_queue_mgmt_ops = {
>  	.ndo_queue_mem_free	= fbnic_queue_mem_free,
>  	.ndo_queue_start	= fbnic_queue_start,
>  	.ndo_queue_stop		= fbnic_queue_stop,
> +	.ndo_validate_qcfg	= fbnic_validate_qcfg,
> +	.supported_params	= QCFG_RX_PAGE_SIZE,
>  };