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, 32 insertions, 0 deletions

diff --git a/include/asm-generic/bitops/sched.h b/include/asm-generic/bitops/sched.h
new file mode 100644
index 000000000..86470cfce
--- /dev/null
+++ b/include/asm-generic/bitops/sched.h
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_GENERIC_BITOPS_SCHED_H_
+#define _ASM_GENERIC_BITOPS_SCHED_H_
+
+#include <linux/compiler.h>	/* unlikely() */
+#include <asm/types.h>
+
+/*
+ * Every architecture must define this function. It's the fastest
+ * way of searching a 100-bit bitmap.  It's guaranteed that at least
+ * one of the 100 bits is cleared.
+ */
+static inline int sched_find_first_bit(const unsigned long *b)
+{
+#if BITS_PER_LONG == 64
+	if (b[0])
+		return __ffs(b[0]);
+	return __ffs(b[1]) + 64;
+#elif BITS_PER_LONG == 32
+	if (b[0])
+		return __ffs(b[0]);
+	if (b[1])
+		return __ffs(b[1]) + 32;
+	if (b[2])
+		return __ffs(b[2]) + 64;
+	return __ffs(b[3]) + 96;
+#else
+#error BITS_PER_LONG not defined
+#endif
+}
+
+#endif /* _ASM_GENERIC_BITOPS_SCHED_H_ */