Merge branch 'net-xdp-handle-frags-with-unreadable-memory'

Jakub Kicinski says:

====================
net: xdp: handle frags with unreadable memory

Make XDP helpers compatible with unreadable memory. This is very
similar to how we handle pfmemalloc frags today. Record the info
in xdp_buf flags as frags get added and then update the skb once
allocated.

This series adds the unreadable memory metadata tracking to drivers
using xdp_build_skb_from*() with no changes on the driver side - hence
the only driver changes here are refactoring. Obviously, unreadable memory
is incompatible with XDP today, but thanks to xdp_build_skb_from_buf()
increasing number of drivers have a unified datapath, whether XDP is
enabled or not.

RFC: https://lore.kernel.org/20250812161528.835855-1-kuba@kernel.org
====================

Link: https://patch.msgid.link/20250905221539.2930285-1-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

1 files changed, 24 insertions, 12 deletions

diff --git a/include/net/xdp.h b/include/net/xdp.h
index af60e11b336c..6fd294fa6841 100644
--- a/include/net/xdp.h
+++ b/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 {
@@ -116,15 +121,19 @@ static __always_inline void xdp_buff_clear_frags_flag(struct xdp_buff *xdp)
 	xdp->flags &= ~XDP_FLAGS_HAS_FRAGS;
 }
 
-static __always_inline bool
-xdp_buff_is_frag_pfmemalloc(const struct xdp_buff *xdp)
+static __always_inline void xdp_buff_set_frag_pfmemalloc(struct xdp_buff *xdp)
 {
-	return !!(xdp->flags & XDP_FLAGS_FRAGS_PF_MEMALLOC);
+	xdp->flags |= XDP_FLAGS_FRAGS_PF_MEMALLOC;
 }
 
-static __always_inline void xdp_buff_set_frag_pfmemalloc(struct xdp_buff *xdp)
+static __always_inline void xdp_buff_set_frag_unreadable(struct xdp_buff *xdp)
 {
-	xdp->flags |= XDP_FLAGS_FRAGS_PF_MEMALLOC;
+	xdp->flags |= XDP_FLAGS_FRAGS_UNREADABLE;
+}
+
+static __always_inline u32 xdp_buff_get_skb_flags(const struct xdp_buff *xdp)
+{
+	return xdp->flags;
 }
 
 static __always_inline void
@@ -271,6 +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;
 }
@@ -294,10 +305,10 @@ static __always_inline bool xdp_frame_has_frags(const struct xdp_frame *frame)
 	return !!(frame->flags & XDP_FLAGS_HAS_FRAGS);
 }
 
-static __always_inline bool
-xdp_frame_is_frag_pfmemalloc(const struct xdp_frame *frame)
+static __always_inline u32
+xdp_frame_get_skb_flags(const struct xdp_frame *frame)
 {
-	return !!(frame->flags & XDP_FLAGS_FRAGS_PF_MEMALLOC);
+	return frame->flags;
 }
 
 #define XDP_BULK_QUEUE_SIZE	16
@@ -334,9 +345,9 @@ static inline void xdp_scrub_frame(struct xdp_frame *frame)
 }
 
 static inline void
-xdp_update_skb_shared_info(struct sk_buff *skb, u8 nr_frags,
-			   unsigned int size, unsigned int truesize,
-			   bool pfmemalloc)
+xdp_update_skb_frags_info(struct sk_buff *skb, u8 nr_frags,
+			  unsigned int size, unsigned int truesize,
+			  u32 xdp_flags)
 {
 	struct skb_shared_info *sinfo = skb_shinfo(skb);
 
@@ -350,7 +361,8 @@ xdp_update_skb_shared_info(struct sk_buff *skb, u8 nr_frags,
 	skb->len += size;
 	skb->data_len += size;
 	skb->truesize += truesize;
-	skb->pfmemalloc |= pfmemalloc;
+	skb->pfmemalloc |= !!(xdp_flags & XDP_FLAGS_FRAGS_PF_MEMALLOC);
+	skb->unreadable |= !!(xdp_flags & XDP_FLAGS_FRAGS_UNREADABLE);
 }
 
 /* Avoids inlining WARN macro in fast-path */