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Date:   Mon, 11 May 2020 15:11:36 +0300
From:   Denis Kirjanov <kda@...ux-powerpc.org>
To:     paul@....org
Cc:     netdev@...r.kernel.org, brouer@...hat.com, jgross@...e.com,
        wei.liu@...nel.org, ilias.apalodimas@...aro.org
Subject: Re: [PATCH net-next v9 2/2] xen networking: add XDP offset adjustment
 to xen-netback

On 5/11/20, Paul Durrant <xadimgnik@...il.com> wrote:
>> -----Original Message-----
>> From: Denis Kirjanov <kda@...ux-powerpc.org>
>> Sent: 11 May 2020 11:22
>> To: netdev@...r.kernel.org
>> Cc: brouer@...hat.com; jgross@...e.com; wei.liu@...nel.org; paul@....org;
>> ilias.apalodimas@...aro.org
>> Subject: [PATCH net-next v9 2/2] xen networking: add XDP offset adjustment
>> to xen-netback
>>
>> the patch basically adds the offset adjustment and netfront
>> state reading to make XDP work on netfront side.
>>
>> Signed-off-by: Denis Kirjanov <denis.kirjanov@...e.com>
>> ---
>>  drivers/net/xen-netback/common.h  |  2 ++
>>  drivers/net/xen-netback/netback.c |  7 +++++++
>>  drivers/net/xen-netback/rx.c      |  7 ++++++-
>>  drivers/net/xen-netback/xenbus.c  | 28 ++++++++++++++++++++++++++++
>>  4 files changed, 43 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/xen-netback/common.h
>> b/drivers/net/xen-netback/common.h
>> index 05847eb..4a148d6 100644
>> --- a/drivers/net/xen-netback/common.h
>> +++ b/drivers/net/xen-netback/common.h
>> @@ -280,6 +280,7 @@ struct xenvif {
>>  	u8 ip_csum:1;
>>  	u8 ipv6_csum:1;
>>  	u8 multicast_control:1;
>> +	u8 xdp_enabled:1;
>>
>>  	/* Is this interface disabled? True when backend discovers
>>  	 * frontend is rogue.
>> @@ -395,6 +396,7 @@ static inline pending_ring_idx_t
>> nr_pending_reqs(struct xenvif_queue *queue)
>>  irqreturn_t xenvif_interrupt(int irq, void *dev_id);
>>
>>  extern bool separate_tx_rx_irq;
>> +extern bool provides_xdp_headroom;
>>
>>  extern unsigned int rx_drain_timeout_msecs;
>>  extern unsigned int rx_stall_timeout_msecs;
>> diff --git a/drivers/net/xen-netback/netback.c
>> b/drivers/net/xen-netback/netback.c
>> index 315dfc6..6dfca72 100644
>> --- a/drivers/net/xen-netback/netback.c
>> +++ b/drivers/net/xen-netback/netback.c
>> @@ -96,6 +96,13 @@
>>  module_param_named(hash_cache_size, xenvif_hash_cache_size, uint, 0644);
>>  MODULE_PARM_DESC(hash_cache_size, "Number of flows in the hash cache");
>>
>> +/* The module parameter tells that we have to put data
>> + * for xen-netfront with the XDP_PACKET_HEADROOM offset
>> + * needed for XDP processing
>> + */
>> +bool provides_xdp_headroom = true;
>> +module_param(provides_xdp_headroom, bool, 0644);
>> +
>>  static void xenvif_idx_release(struct xenvif_queue *queue, u16
>> pending_idx,
>>  			       u8 status);
>>
>> diff --git a/drivers/net/xen-netback/rx.c b/drivers/net/xen-netback/rx.c
>> index ef58870..c97c98e 100644
>> --- a/drivers/net/xen-netback/rx.c
>> +++ b/drivers/net/xen-netback/rx.c
>> @@ -33,6 +33,11 @@
>>  #include <xen/xen.h>
>>  #include <xen/events.h>
>>
>> +static int xenvif_rx_xdp_offset(struct xenvif *vif)
>> +{
>> +	return vif->xdp_enabled ? XDP_PACKET_HEADROOM : 0;
>> +}
>> +
>>  static bool xenvif_rx_ring_slots_available(struct xenvif_queue *queue)
>>  {
>>  	RING_IDX prod, cons;
>> @@ -356,7 +361,7 @@ static void xenvif_rx_data_slot(struct xenvif_queue
>> *queue,
>>  				struct xen_netif_rx_request *req,
>>  				struct xen_netif_rx_response *rsp)
>>  {
>> -	unsigned int offset = 0;
>> +	unsigned int offset = xenvif_rx_xdp_offset(queue->vif);
>>  	unsigned int flags;
>>
>>  	do {
>> diff --git a/drivers/net/xen-netback/xenbus.c
>> b/drivers/net/xen-netback/xenbus.c
>> index 286054b..d447191 100644
>> --- a/drivers/net/xen-netback/xenbus.c
>> +++ b/drivers/net/xen-netback/xenbus.c
>> @@ -393,6 +393,20 @@ static void set_backend_state(struct backend_info
>> *be,
>>  	}
>>  }
>>
>> +static void read_xenbus_frontend_xdp(struct backend_info *be,
>> +				     struct xenbus_device *dev)
>> +{
>> +	struct xenvif *vif = be->vif;
>> +	unsigned int val;
>> +	int err;
>> +
>> +	err = xenbus_scanf(XBT_NIL, dev->otherend,
>> +			   "feature-xdp", "%u", &val);
>> +	if (err != 1)
>> +		return;
>> +	vif->xdp_enabled = val;
>> +}
>> +
>>  /**
>>   * Callback received when the frontend's state changes.
>>   */
>> @@ -417,6 +431,11 @@ static void frontend_changed(struct xenbus_device
>> *dev,
>>  		set_backend_state(be, XenbusStateConnected);
>>  		break;
>>
>> +	case XenbusStateReconfiguring:
>> +		read_xenbus_frontend_xdp(be, dev);
>
> I think this being the only call to read_xenbus_frontend_xdp() is still a
> problem. What happens if netback is reloaded against a
> netfront that has already enabled 'feature-xdp'? AFAICT vif->xdp_enabled
> would remain false after the reload.

in this case xennect_connect() should call talk_to_netback()
and the function will restore the state from info->netfront_xdp_enabled

>
>   Paul
>
>> +		xenbus_switch_state(dev, XenbusStateReconfigured);
>> +		break;
>> +
>>  	case XenbusStateClosing:
>>  		set_backend_state(be, XenbusStateClosing);
>>  		break;
>> @@ -1036,6 +1055,15 @@ static int netback_probe(struct xenbus_device
>> *dev,
>>  			goto abort_transaction;
>>  		}
>>
>> +		/* we can adjust a headroom for netfront XDP processing */
>> +		err = xenbus_printf(xbt, dev->nodename,
>> +				    "feature-xdp-headroom", "%d",
>> +				    provides_xdp_headroom);
>> +		if (err) {
>> +			message = "writing feature-xdp-headroom";
>> +			goto abort_transaction;
>> +		}
>> +
>>  		/* We don't support rx-flip path (except old guests who
>>  		 * don't grok this feature flag).
>>  		 */
>> --
>> 1.8.3.1
>
>
>

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