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, 45 insertions, 0 deletions

diff --git a/drivers/md/dm-vdo/permassert.h b/drivers/md/dm-vdo/permassert.h
new file mode 100644
index 000000000..c34f2ba65
--- /dev/null
+++ b/drivers/md/dm-vdo/permassert.h
@@ -0,0 +1,45 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2023 Red Hat
+ */
+
+#ifndef PERMASSERT_H
+#define PERMASSERT_H
+
+#include <linux/compiler.h>
+
+#include "errors.h"
+
+/* Utilities for asserting that certain conditions are met */
+
+#define STRINGIFY(X) #X
+
+/*
+ * A hack to apply the "warn if unused" attribute to an integral expression.
+ *
+ * Since GCC doesn't propagate the warn_unused_result attribute to conditional expressions
+ * incorporating calls to functions with that attribute, this function can be used to wrap such an
+ * expression. With optimization enabled, this function contributes no additional instructions, but
+ * the warn_unused_result attribute still applies to the code calling it.
+ */
+static inline int __must_check vdo_must_use(int value)
+{
+	return value;
+}
+
+/* Assert that an expression is true and return an error if it is not. */
+#define VDO_ASSERT(expr, ...) vdo_must_use(__VDO_ASSERT(expr, __VA_ARGS__))
+
+/* Log a message if the expression is not true. */
+#define VDO_ASSERT_LOG_ONLY(expr, ...) __VDO_ASSERT(expr, __VA_ARGS__)
+
+#define __VDO_ASSERT(expr, ...)				      \
+	(likely(expr) ? VDO_SUCCESS			      \
+		      : vdo_assertion_failed(STRINGIFY(expr), __FILE__, __LINE__, __VA_ARGS__))
+
+/* Log an assertion failure message. */
+int vdo_assertion_failed(const char *expression_string, const char *file_name,
+			 int line_number, const char *format, ...)
+	__printf(4, 5);
+
+#endif /* PERMASSERT_H */