net: add get_netmem/put_netmem support

Currently net_iovs support only pp ref counts, and do not support a
page ref equivalent.

This is fine for the RX path as net_iovs are used exclusively with the
pp and only pp refcounting is needed there. The TX path however does not
use pp ref counts, thus, support for get_page/put_page equivalent is
needed for netmem.

Support get_netmem/put_netmem. Check the type of the netmem before
passing it to page or net_iov specific code to obtain a page ref
equivalent.

For dmabuf net_iovs, we obtain a ref on the underlying binding. This
ensures the entire binding doesn't disappear until all the net_iovs have
been put_netmem'ed. We do not need to track the refcount of individual
dmabuf net_iovs as we don't allocate/free them from a pool similar to
what the buddy allocator does for pages.

This code is written to be extensible by other net_iov implementers.
get_netmem/put_netmem will check the type of the netmem and route it to
the correct helper:

pages -> [get|put]_page()
dmabuf net_iovs -> net_devmem_[get|put]_net_iov()
new net_iovs ->	new helpers

Signed-off-by: Mina Almasry <almasrymina@google.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20250508004830.4100853-3-almasrymina@google.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

1 files changed, 30 insertions, 0 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index d73ad79fe739d..00c22bce98e44 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -89,6 +89,7 @@
 #include <linux/textsearch.h>
 
 #include "dev.h"
+#include "devmem.h"
 #include "netmem_priv.h"
 #include "sock_destructor.h"
 
@@ -7313,3 +7314,32 @@ bool csum_and_copy_from_iter_full(void *addr, size_t bytes,
 	return false;
 }
 EXPORT_SYMBOL(csum_and_copy_from_iter_full);
+
+void get_netmem(netmem_ref netmem)
+{
+	struct net_iov *niov;
+
+	if (netmem_is_net_iov(netmem)) {
+		niov = netmem_to_net_iov(netmem);
+		if (net_is_devmem_iov(niov))
+			net_devmem_get_net_iov(netmem_to_net_iov(netmem));
+		return;
+	}
+	get_page(netmem_to_page(netmem));
+}
+EXPORT_SYMBOL(get_netmem);
+
+void put_netmem(netmem_ref netmem)
+{
+	struct net_iov *niov;
+
+	if (netmem_is_net_iov(netmem)) {
+		niov = netmem_to_net_iov(netmem);
+		if (net_is_devmem_iov(niov))
+			net_devmem_put_net_iov(netmem_to_net_iov(netmem));
+		return;
+	}
+
+	put_page(netmem_to_page(netmem));
+}
+EXPORT_SYMBOL(put_netmem);