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, 14 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-devices-sun b/Documentation/ABI/testing/sysfs-devices-sun
new file mode 100644
index 000000000..625ce4b63
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-devices-sun
@@ -0,0 +1,14 @@
+What:		/sys/devices/.../sun
+Date:		October 2012
+Contact:	Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
+Description:
+		The file contains a Slot-unique ID which provided by the _SUN
+		method in the ACPI namespace. The value is written in Advanced
+		Configuration and Power Interface Specification as follows:
+
+		"The _SUN value is required to be unique among the slots of
+		the same type. It is also recommended that this number match
+		the slot number printed on the physical slot whenever possible."
+
+		So reading the sysfs file, we can identify a physical position
+		of the slot in the system.