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, 105 insertions, 0 deletions

diff --git a/lib/ratelimit.c b/lib/ratelimit.c
new file mode 100644
index 000000000..e2d65d3b1
--- /dev/null
+++ b/lib/ratelimit.c
@@ -0,0 +1,105 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * ratelimit.c - Do something with rate limit.
+ *
+ * Isolated from kernel/printk.c by Dave Young <hidave.darkstar@gmail.com>
+ *
+ * 2008-05-01 rewrite the function and use a ratelimit_state data struct as
+ * parameter. Now every user can use their own standalone ratelimit_state.
+ */
+
+#include <linux/ratelimit.h>
+#include <linux/jiffies.h>
+#include <linux/export.h>
+
+/*
+ * __ratelimit - rate limiting
+ * @rs: ratelimit_state data
+ * @func: name of calling function
+ *
+ * This enforces a rate limit: not more than @rs->burst callbacks
+ * in every @rs->interval
+ *
+ * RETURNS:
+ * 0 means callbacks will be suppressed.
+ * 1 means go ahead and do it.
+ */
+int ___ratelimit(struct ratelimit_state *rs, const char *func)
+{
+	/* Paired with WRITE_ONCE() in .proc_handler().
+	 * Changing two values separately could be inconsistent
+	 * and some message could be lost.  (See: net_ratelimit_state).
+	 */
+	int interval = READ_ONCE(rs->interval);
+	int burst = READ_ONCE(rs->burst);
+	unsigned long flags;
+	int ret = 0;
+
+	/*
+	 * Zero interval says never limit, otherwise, non-positive burst
+	 * says always limit.
+	 */
+	if (interval <= 0 || burst <= 0) {
+		WARN_ONCE(interval < 0 || burst < 0, "Negative interval (%d) or burst (%d): Uninitialized ratelimit_state structure?\n", interval, burst);
+		ret = interval == 0 || burst > 0;
+		if (!(READ_ONCE(rs->flags) & RATELIMIT_INITIALIZED) || (!interval && !burst) ||
+		    !raw_spin_trylock_irqsave(&rs->lock, flags))
+			goto nolock_ret;
+
+		/* Force re-initialization once re-enabled. */
+		rs->flags &= ~RATELIMIT_INITIALIZED;
+		goto unlock_ret;
+	}
+
+	/*
+	 * If we contend on this state's lock then just check if
+	 * the current burst is used or not. It might cause
+	 * false positive when we are past the interval and
+	 * the current lock owner is just about to reset it.
+	 */
+	if (!raw_spin_trylock_irqsave(&rs->lock, flags)) {
+		if (READ_ONCE(rs->flags) & RATELIMIT_INITIALIZED &&
+		    atomic_read(&rs->rs_n_left) > 0 && atomic_dec_return(&rs->rs_n_left) >= 0)
+			ret = 1;
+		goto nolock_ret;
+	}
+
+	if (!(rs->flags & RATELIMIT_INITIALIZED)) {
+		rs->begin = jiffies;
+		rs->flags |= RATELIMIT_INITIALIZED;
+		atomic_set(&rs->rs_n_left, rs->burst);
+	}
+
+	if (time_is_before_jiffies(rs->begin + interval)) {
+		int m;
+
+		/*
+		 * Reset rs_n_left ASAP to reduce false positives
+		 * in parallel calls, see above.
+		 */
+		atomic_set(&rs->rs_n_left, rs->burst);
+		rs->begin = jiffies;
+
+		if (!(rs->flags & RATELIMIT_MSG_ON_RELEASE)) {
+			m = ratelimit_state_reset_miss(rs);
+			if (m) {
+				printk_deferred(KERN_WARNING
+						"%s: %d callbacks suppressed\n", func, m);
+			}
+		}
+	}
+
+	/* Note that the burst might be taken by a parallel call. */
+	if (atomic_read(&rs->rs_n_left) > 0 && atomic_dec_return(&rs->rs_n_left) >= 0)
+		ret = 1;
+
+unlock_ret:
+	raw_spin_unlock_irqrestore(&rs->lock, flags);
+
+nolock_ret:
+	if (!ret)
+		ratelimit_state_inc_miss(rs);
+
+	return ret;
+}
+EXPORT_SYMBOL(___ratelimit);