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, 73 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-pps b/Documentation/ABI/testing/sysfs-pps
new file mode 100644
index 000000000..25028c7bc
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-pps
@@ -0,0 +1,73 @@
+What:		/sys/class/pps/
+Date:		February 2008
+Contact:	Rodolfo Giometti <giometti@linux.it>
+Description:
+		The /sys/class/pps/ directory will contain files and
+		directories that will provide a unified interface to
+		the PPS sources.
+
+What:		/sys/class/pps/ppsX/
+Date:		February 2008
+Contact:	Rodolfo Giometti <giometti@linux.it>
+Description:
+		The /sys/class/pps/ppsX/ directory is related to X-th
+		PPS source into the system. Each directory will
+		contain files to manage and control its PPS source.
+
+What:		/sys/class/pps/ppsX/assert
+Date:		February 2008
+Contact:	Rodolfo Giometti <giometti@linux.it>
+Description:
+		The /sys/class/pps/ppsX/assert file reports the assert events
+		and the assert sequence number of the X-th source in the form:
+
+			<secs>.<nsec>#<sequence>
+
+		If the source has no assert events the content of this file
+		is empty.
+
+What:		/sys/class/pps/ppsX/clear
+Date:		February 2008
+Contact:	Rodolfo Giometti <giometti@linux.it>
+Description:
+		The /sys/class/pps/ppsX/clear file reports the clear events
+		and the clear sequence number of the X-th source in the form:
+
+			<secs>.<nsec>#<sequence>
+
+		If the source has no clear events the content of this file
+		is empty.
+
+What:		/sys/class/pps/ppsX/mode
+Date:		February 2008
+Contact:	Rodolfo Giometti <giometti@linux.it>
+Description:
+		The /sys/class/pps/ppsX/mode file reports the functioning
+		mode of the X-th source in hexadecimal encoding.
+
+		Please, refer to linux/include/linux/pps.h for further
+		info.
+
+What:		/sys/class/pps/ppsX/echo
+Date:		February 2008
+Contact:	Rodolfo Giometti <giometti@linux.it>
+Description:
+		The /sys/class/pps/ppsX/echo file reports if the X-th does
+		or does not support an "echo" function.
+
+What:		/sys/class/pps/ppsX/name
+Date:		February 2008
+Contact:	Rodolfo Giometti <giometti@linux.it>
+Description:
+		The /sys/class/pps/ppsX/name file reports the name of the
+		X-th source.
+
+What:		/sys/class/pps/ppsX/path
+Date:		February 2008
+Contact:	Rodolfo Giometti <giometti@linux.it>
+Description:
+		The /sys/class/pps/ppsX/path file reports the path name of
+		the device connected with the X-th source.
+
+		If the source is not connected with any device the content
+		of this file is empty.