KVM: Don't pre-reserve xarray entries when storing empty/NULL attributesgrafted

Skip the xarray reservation loop when clearing all memory attributes, as
storing NULL only erases the entry and never needs to allocate, so no
reservation (and no cleanup of a failed one) is required in that case.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: David Ballesteros <davimaba.v@proton.me>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com
[sean: split to separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 96 insertions, 0 deletions

diff --git a/net/batman-adv/bitarray.c b/net/batman-adv/bitarray.c
new file mode 100644
index 000000000..f814756d9
--- /dev/null
+++ b/net/batman-adv/bitarray.c
@@ -0,0 +1,96 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) B.A.T.M.A.N. contributors:
+ *
+ * Simon Wunderlich, Marek Lindner
+ */
+
+#include "bitarray.h"
+#include "main.h"
+
+#include <linux/bitmap.h>
+
+#include "log.h"
+
+/**
+ * batadv_bitmap_shift_left() - shift the sequence number bitmap left
+ * @seq_bits: the sequence number bitmap to shift
+ * @n: number of positions to shift left
+ *
+ * Shift @seq_bits by @n positions. No-op if @n is not within the bounds of
+ * the bitmap.
+ */
+static void batadv_bitmap_shift_left(unsigned long *seq_bits, s32 n)
+{
+	if (n <= 0 || n >= BATADV_TQ_LOCAL_WINDOW_SIZE)
+		return;
+
+	bitmap_shift_left(seq_bits, seq_bits, n, BATADV_TQ_LOCAL_WINDOW_SIZE);
+}
+
+/**
+ * batadv_bit_get_packet() - receive and process one packet within the sequence
+ *  number window
+ * @priv: the bat priv with all the mesh interface information
+ * @seq_bits: pointer to the sequence number bitmap of received packets
+ * @seq_num_diff: difference between the current/received sequence number and
+ *  the last sequence number
+ * @set_mark: whether this packet should be marked in seq_bits
+ *
+ * Return: true if the window was moved (either new or very old),
+ *  false if the window was not moved/shifted.
+ */
+bool batadv_bit_get_packet(void *priv, unsigned long *seq_bits,
+			   s32 seq_num_diff, int set_mark)
+{
+	struct batadv_priv *bat_priv = priv;
+
+	/* sequence number is slightly older. We already got a sequence number
+	 * higher than this one, so we just mark it.
+	 */
+	if (seq_num_diff <= 0 && seq_num_diff > -BATADV_TQ_LOCAL_WINDOW_SIZE) {
+		if (set_mark)
+			batadv_set_bit(seq_bits, -seq_num_diff);
+		return false;
+	}
+
+	/* sequence number is slightly newer, so we shift the window and
+	 * set the mark if required
+	 */
+	if (seq_num_diff > 0 && seq_num_diff < BATADV_TQ_LOCAL_WINDOW_SIZE) {
+		batadv_bitmap_shift_left(seq_bits, seq_num_diff);
+
+		if (set_mark)
+			batadv_set_bit(seq_bits, 0);
+		return true;
+	}
+
+	/* sequence number is much newer, probably missed a lot of packets */
+	if (seq_num_diff >= BATADV_TQ_LOCAL_WINDOW_SIZE &&
+	    seq_num_diff < BATADV_EXPECTED_SEQNO_RANGE) {
+		batadv_dbg(BATADV_DBG_BATMAN, bat_priv,
+			   "We missed a lot of packets (%i) !\n",
+			   seq_num_diff - 1);
+		bitmap_zero(seq_bits, BATADV_TQ_LOCAL_WINDOW_SIZE);
+		if (set_mark)
+			batadv_set_bit(seq_bits, 0);
+		return true;
+	}
+
+	/* received a much older packet. The other host either restarted
+	 * or the old packet got delayed somewhere in the network. The
+	 * packet should be dropped without calling this function if the
+	 * seqno window is protected.
+	 *
+	 * seq_num_diff <= -BATADV_TQ_LOCAL_WINDOW_SIZE
+	 * or
+	 * seq_num_diff >= BATADV_EXPECTED_SEQNO_RANGE
+	 */
+	batadv_dbg(BATADV_DBG_BATMAN, bat_priv,
+		   "Other host probably restarted!\n");
+
+	bitmap_zero(seq_bits, BATADV_TQ_LOCAL_WINDOW_SIZE);
+	if (set_mark)
+		batadv_set_bit(seq_bits, 0);
+
+	return true;
+}