[net-next PATCH v5 2/6] net: xdp: add invalid buffer warning

[John Fastabend <john.fastabend@gmail.com>]

This adds a warning for drivers to use when encountering an invalid
buffer for XDP. For normal cases this should not happen but to catch
this in virtual/qemu setups that I may not have expected from the
emulation layer having a standard warning is useful.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
---
 include/linux/filter.h |    1 +
 net/core/filter.c      |    6 ++++++
 2 files changed, 7 insertions(+)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index f078d2b..860f953 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -600,6 +600,7 @@ int sk_get_filter(struct sock *sk, struct sock_filter __user *filter,
 struct bpf_prog *bpf_patch_insn_single(struct bpf_prog *prog, u32 off,
 				       const struct bpf_insn *patch, u32 len);
 void bpf_warn_invalid_xdp_action(u32 act);
+void bpf_warn_invalid_xdp_buffer(void);
 
 #ifdef CONFIG_BPF_JIT
 extern int bpf_jit_enable;
diff --git a/net/core/filter.c b/net/core/filter.c
index b751202..849f23d 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2948,6 +2948,12 @@ void bpf_warn_invalid_xdp_action(u32 act)
 }
 EXPORT_SYMBOL_GPL(bpf_warn_invalid_xdp_action);
 
+void bpf_warn_invalid_xdp_buffer(void)
+{
+	WARN_ONCE(1, "Illegal XDP buffer encountered, expect throughput degradation\n");
+}
+EXPORT_SYMBOL_GPL(bpf_warn_invalid_xdp_buffer);
+
 static u32 sk_filter_convert_ctx_access(enum bpf_access_type type, int dst_reg,
 					int src_reg, int ctx_off,
 					struct bpf_insn *insn_buf,