> -----Original Message-----
> From: Denis Kirjanov <k...@linux-powerpc.org>
> Sent: 11 May 2020 13:12
> To: p...@xen.org
> Cc: netdev@vger.kernel.org; bro...@redhat.com; jgr...@suse.com;
> wei....@kernel.org;
> ilias.apalodi...@linaro.org
> Subject: Re: [PATCH net-next v9 2/2] xen networking: add XDP offset
> adjustment to xen-netback
>
> On 5/11/20, Paul Durrant <xadimg...@gmail.com> wrote:
> >> -----Original Message-----
> >> From: Denis Kirjanov <k...@linux-powerpc.org>
> >> Sent: 11 May 2020 11:22
> >> To: netdev@vger.kernel.org
> >> Cc: bro...@redhat.com; jgr...@suse.com; wei....@kernel.org; p...@xen.org;
> >> ilias.apalodi...@linaro.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.kirja...@suse.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.
Paul
