net: xdp: handle frags with unreadable memory

We don't expect frags with unreadable memory to be presented
to XDP programs today, but the XDP helpers are designed to be
usable whether XDP is enabled or not. Support handling frags
with unreadable memory.

Signed-off-by: Jakub Kicinski <[email protected]>
Link: https://patch.msgid.link/[email protected]
Acked-by: Stanislav Fomichev <[email protected]>
Reviewed-by: Alexander Lobakin <[email protected]>
Signed-off-by: Paolo Abeni <[email protected]>

Author: kuba-moo

include/net/xdp.h

@@ -76,6 +76,11 @@ enum xdp_buff_flags {
 	XDP_FLAGS_FRAGS_PF_MEMALLOC	= BIT(1), /* xdp paged memory is under
 						   * pressure
 						   */
+	/* frags have unreadable mem, this can't be true for real XDP packets,
+	 * but drivers may use XDP helpers to construct Rx pkt state even when
+	 * XDP program is not attached.
+	 */
+	XDP_FLAGS_FRAGS_UNREADABLE	= BIT(2),
 };
 
 struct xdp_buff {
@@ -121,6 +126,11 @@ static __always_inline void xdp_buff_set_frag_pfmemalloc(struct xdp_buff *xdp)
 	xdp->flags |= XDP_FLAGS_FRAGS_PF_MEMALLOC;
 }
 
+static __always_inline void xdp_buff_set_frag_unreadable(struct xdp_buff *xdp)
+{
+	xdp->flags |= XDP_FLAGS_FRAGS_UNREADABLE;
+}
+
 static __always_inline u32 xdp_buff_get_skb_flags(const struct xdp_buff *xdp)
 {
 	return xdp->flags;
@@ -270,6 +280,8 @@ static inline bool xdp_buff_add_frag(struct xdp_buff *xdp, netmem_ref netmem,
 
 	if (unlikely(netmem_is_pfmemalloc(netmem)))
 		xdp_buff_set_frag_pfmemalloc(xdp);
+	if (unlikely(netmem_is_net_iov(netmem)))
+		xdp_buff_set_frag_unreadable(xdp);
 
 	return true;
 }
@@ -350,6 +362,7 @@ xdp_update_skb_frags_info(struct sk_buff *skb, u8 nr_frags,
 	skb->data_len += size;
 	skb->truesize += truesize;
 	skb->pfmemalloc |= !!(xdp_flags & XDP_FLAGS_FRAGS_PF_MEMALLOC);
+	skb->unreadable |= !!(xdp_flags & XDP_FLAGS_FRAGS_UNREADABLE);
 }
 
 /* Avoids inlining WARN macro in fast-path */