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, 31 insertions, 0 deletions

diff --git a/include/vdso/page.h b/include/vdso/page.h
new file mode 100644
index 000000000..bc47186c0
--- /dev/null
+++ b/include/vdso/page.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __VDSO_PAGE_H
+#define __VDSO_PAGE_H
+
+#include <uapi/linux/const.h>
+
+/*
+ * PAGE_SHIFT determines the page size.
+ *
+ * Note: This definition is required because PAGE_SHIFT is used
+ * in several places throughout the codebase.
+ */
+#define PAGE_SHIFT      CONFIG_PAGE_SHIFT
+
+#define PAGE_SIZE	(_AC(1,UL) << CONFIG_PAGE_SHIFT)
+
+#if !defined(CONFIG_64BIT)
+/*
+ * Applies only to 32-bit architectures.
+ *
+ * Subtle: (1 << CONFIG_PAGE_SHIFT) is an int, not an unsigned long.
+ * So if we assign PAGE_MASK to a larger type it gets extended the
+ * way we want (i.e. with 1s in the high bits) while masking a
+ * 64-bit value such as phys_addr_t.
+ */
+#define PAGE_MASK	(~((1 << CONFIG_PAGE_SHIFT) - 1))
+#else
+#define PAGE_MASK	(~(PAGE_SIZE - 1))
+#endif
+
+#endif	/* __VDSO_PAGE_H */