[RFC bpf-next 3/6] xsk: don't allow umem replace at stack level

[Jakub Kicinski]

Currently drivers have to check if they already have a umem
installed for a given queue and return an error if so.  Make
better use of XDP_QUERY_XSK_UMEM and move this functionality
to the core.

We need to keep rtnl across the calls now.

Signed-off-by: Jakub Kicinski <jakub.kicin...@netronome.com>
Reviewed-by: Quentin Monnet <quentin.mon...@netronome.com>
---
 include/linux/netdevice.h |  7 ++++---
 net/xdp/xdp_umem.c        | 37 ++++++++++++++++++++++++++++---------
 2 files changed, 32 insertions(+), 12 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 6717dc7e8fbf..a5a34f0fb485 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -872,10 +872,10 @@ struct netdev_bpf {
                struct {
                        struct bpf_offloaded_map *offmap;
                };
-               /* XDP_SETUP_XSK_UMEM */
+               /* XDP_QUERY_XSK_UMEM, XDP_SETUP_XSK_UMEM */
                struct {
-                       struct xdp_umem *umem;
-                       u16 queue_id;
+                       struct xdp_umem *umem; /* out for query*/
+                       u16 queue_id; /* in for query */
                } xsk;
        };
 };
@@ -3566,6 +3566,7 @@ int dev_change_xdp_fd(struct net_device *dev, struct 
netlink_ext_ack *extack,
                      int fd, u32 flags);
 u32 __dev_xdp_query(struct net_device *dev, bpf_op_t xdp_op,
                    enum bpf_netdev_command cmd);
+int xdp_umem_query(struct net_device *dev, u16 queue_id);
 
 int __dev_forward_skb(struct net_device *dev, struct sk_buff *skb);
 int dev_forward_skb(struct net_device *dev, struct sk_buff *skb);
diff --git a/net/xdp/xdp_umem.c b/net/xdp/xdp_umem.c
index c199d66b5f3f..911ca6d3cb5a 100644
--- a/net/xdp/xdp_umem.c
+++ b/net/xdp/xdp_umem.c
@@ -11,6 +11,8 @@
 #include <linux/slab.h>
 #include <linux/bpf.h>
 #include <linux/mm.h>
+#include <linux/netdevice.h>
+#include <linux/rtnetlink.h>
 
 #include "xdp_umem.h"
 #include "xsk_queue.h"
@@ -40,6 +42,21 @@ void xdp_del_sk_umem(struct xdp_umem *umem, struct xdp_sock 
*xs)
        }
 }
 
+int xdp_umem_query(struct net_device *dev, u16 queue_id)
+{
+       struct netdev_bpf bpf;
+
+       ASSERT_RTNL();
+
+       memset(&bpf, 0, sizeof(bpf));
+       bpf.command = XDP_QUERY_XSK_UMEM;
+       bpf.xsk.queue_id = queue_id;
+
+       if (!dev->netdev_ops->ndo_bpf)
+               return 0;
+       return dev->netdev_ops->ndo_bpf(dev, &bpf) ?: !!bpf.xsk.umem;
+}
+
 int xdp_umem_assign_dev(struct xdp_umem *umem, struct net_device *dev,
                        u32 queue_id, u16 flags)
 {
@@ -62,28 +79,30 @@ int xdp_umem_assign_dev(struct xdp_umem *umem, struct 
net_device *dev,
        bpf.command = XDP_QUERY_XSK_UMEM;
 
        rtnl_lock();
-       err = dev->netdev_ops->ndo_bpf(dev, &bpf);
-       rtnl_unlock();
-
-       if (err)
-               return force_zc ? -ENOTSUPP : 0;
+       err = xdp_umem_query(dev, queue_id);
+       if (err) {
+               err = err < 0 ? -ENOTSUPP : -EBUSY;
+               goto err_rtnl_unlock;
+       }
 
        bpf.command = XDP_SETUP_XSK_UMEM;
        bpf.xsk.umem = umem;
        bpf.xsk.queue_id = queue_id;
 
-       rtnl_lock();
        err = dev->netdev_ops->ndo_bpf(dev, &bpf);
-       rtnl_unlock();
-
        if (err)
-               return force_zc ? err : 0; /* fail or fallback */
+               goto err_rtnl_unlock;
+       rtnl_unlock();
 
        dev_hold(dev);
        umem->dev = dev;
        umem->queue_id = queue_id;
        umem->zc = true;
        return 0;
+
+err_rtnl_unlock:
+       rtnl_unlock();
+       return force_zc ? err : 0; /* fail or fallback */
 }
 
 static void xdp_umem_clear_dev(struct xdp_umem *umem)
-- 
2.17.1