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Date:   Mon, 11 May 2020 20:21:49 +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 13:12
>> 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
>>
>
> No. You're assuming the frontend is aware the backend has been reloaded. It
> is not.

Hi Paul,

I've tried to unbind/bind the device and I can see that the variable
is set properly:

with enabled XDP:
<7>[  622.177935] xen_netback:backend_switch_state: backend/vif/2/0 -> InitWait
<7>[  622.179917] xen_netback:frontend_changed:
/local/domain/2/device/vif/0 -> Connected
<6>[  622.187393] vif vif-2-0 vif2.0: Guest Rx ready
<7>[  622.188451] xen_netback:backend_switch_state: backend/vif/2/0 -> Connected

localhost:/sys/bus/xen-backend/drivers/vif # xenstore-ls | grep xdp
       feature-xdp-headroom = "1"
      feature-xdp = "1"

and with disabled:

7>[  758.216792] xen_netback:frontend_changed:
/local/domain/2/device/vif/0 -> Reconfiguring
<7>[  758.218741] xen_netback:frontend_changed:
/local/domain/2/device/vif/0 -> Connected
<7>[  784.177247] xen_netback:backend_switch_state: backend/vif/2/0 -> InitWait
<7>[  784.180101] xen_netback:frontend_changed:
/local/domain/2/device/vif/0 -> Connected
<6>[  784.187927] vif vif-2-0 vif2.0: Guest Rx ready
<7>[  784.188890] xen_netback:backend_switch_state: backend/vif/2/0 -> Connected

localhost:/sys/bus/xen-backend/drivers/vif # xenstore-ls | grep xdp
       feature-xdp-headroom = "1"
      feature-xdp = "0"




>
>   Paul
>
>
>

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