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, 116 insertions, 0 deletions

diff --git a/lib/test_ref_tracker.c b/lib/test_ref_tracker.c
new file mode 100644
index 000000000..b983ceb12
--- /dev/null
+++ b/lib/test_ref_tracker.c
@@ -0,0 +1,116 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Reference tracker self test.
+ *
+ * Copyright (c) 2021 Eric Dumazet <edumazet@google.com>
+ */
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/delay.h>
+#include <linux/ref_tracker.h>
+#include <linux/slab.h>
+#include <linux/timer.h>
+
+static struct ref_tracker_dir ref_dir;
+static struct ref_tracker *tracker[20];
+
+#define TRT_ALLOC(X) static noinline void 				\
+	alloctest_ref_tracker_alloc##X(struct ref_tracker_dir *dir, 	\
+				    struct ref_tracker **trackerp)	\
+	{								\
+		ref_tracker_alloc(dir, trackerp, GFP_KERNEL);		\
+	}
+
+TRT_ALLOC(1)
+TRT_ALLOC(2)
+TRT_ALLOC(3)
+TRT_ALLOC(4)
+TRT_ALLOC(5)
+TRT_ALLOC(6)
+TRT_ALLOC(7)
+TRT_ALLOC(8)
+TRT_ALLOC(9)
+TRT_ALLOC(10)
+TRT_ALLOC(11)
+TRT_ALLOC(12)
+TRT_ALLOC(13)
+TRT_ALLOC(14)
+TRT_ALLOC(15)
+TRT_ALLOC(16)
+TRT_ALLOC(17)
+TRT_ALLOC(18)
+TRT_ALLOC(19)
+
+#undef TRT_ALLOC
+
+static noinline void
+alloctest_ref_tracker_free(struct ref_tracker_dir *dir,
+			   struct ref_tracker **trackerp)
+{
+	ref_tracker_free(dir, trackerp);
+}
+
+
+static struct timer_list test_ref_tracker_timer;
+static atomic_t test_ref_timer_done = ATOMIC_INIT(0);
+
+static void test_ref_tracker_timer_func(struct timer_list *t)
+{
+	ref_tracker_alloc(&ref_dir, &tracker[0], GFP_ATOMIC);
+	atomic_set(&test_ref_timer_done, 1);
+}
+
+static int __init test_ref_tracker_init(void)
+{
+	int i;
+
+	ref_tracker_dir_init(&ref_dir, 100, "selftest");
+
+	timer_setup(&test_ref_tracker_timer, test_ref_tracker_timer_func, 0);
+	mod_timer(&test_ref_tracker_timer, jiffies + 1);
+
+	alloctest_ref_tracker_alloc1(&ref_dir, &tracker[1]);
+	alloctest_ref_tracker_alloc2(&ref_dir, &tracker[2]);
+	alloctest_ref_tracker_alloc3(&ref_dir, &tracker[3]);
+	alloctest_ref_tracker_alloc4(&ref_dir, &tracker[4]);
+	alloctest_ref_tracker_alloc5(&ref_dir, &tracker[5]);
+	alloctest_ref_tracker_alloc6(&ref_dir, &tracker[6]);
+	alloctest_ref_tracker_alloc7(&ref_dir, &tracker[7]);
+	alloctest_ref_tracker_alloc8(&ref_dir, &tracker[8]);
+	alloctest_ref_tracker_alloc9(&ref_dir, &tracker[9]);
+	alloctest_ref_tracker_alloc10(&ref_dir, &tracker[10]);
+	alloctest_ref_tracker_alloc11(&ref_dir, &tracker[11]);
+	alloctest_ref_tracker_alloc12(&ref_dir, &tracker[12]);
+	alloctest_ref_tracker_alloc13(&ref_dir, &tracker[13]);
+	alloctest_ref_tracker_alloc14(&ref_dir, &tracker[14]);
+	alloctest_ref_tracker_alloc15(&ref_dir, &tracker[15]);
+	alloctest_ref_tracker_alloc16(&ref_dir, &tracker[16]);
+	alloctest_ref_tracker_alloc17(&ref_dir, &tracker[17]);
+	alloctest_ref_tracker_alloc18(&ref_dir, &tracker[18]);
+	alloctest_ref_tracker_alloc19(&ref_dir, &tracker[19]);
+
+	/* free all trackers but first 0 and 1. */
+	for (i = 2; i < ARRAY_SIZE(tracker); i++)
+		alloctest_ref_tracker_free(&ref_dir, &tracker[i]);
+
+	/* Attempt to free an already freed tracker. */
+	alloctest_ref_tracker_free(&ref_dir, &tracker[2]);
+
+	while (!atomic_read(&test_ref_timer_done))
+		msleep(1);
+
+	/* This should warn about tracker[0] & tracker[1] being not freed. */
+	ref_tracker_dir_exit(&ref_dir);
+
+	return 0;
+}
+
+static void __exit test_ref_tracker_exit(void)
+{
+}
+
+module_init(test_ref_tracker_init);
+module_exit(test_ref_tracker_exit);
+
+MODULE_DESCRIPTION("Reference tracker self test");
+MODULE_LICENSE("GPL v2");