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, 69 insertions, 0 deletions

diff --git a/scripts/extract-ikconfig b/scripts/extract-ikconfig
new file mode 100755
index 000000000..8df33e7d6
--- /dev/null
+++ b/scripts/extract-ikconfig
@@ -0,0 +1,69 @@
+#!/bin/sh
+# ----------------------------------------------------------------------
+# extract-ikconfig - Extract the .config file from a kernel image
+#
+# This will only work when the kernel was compiled with CONFIG_IKCONFIG.
+#
+# The obscure use of the "tr" filter is to work around older versions of
+# "grep" that report the byte offset of the line instead of the pattern.
+#
+# (c) 2009,2010 Dick Streefland <dick@streefland.net>
+# Licensed under the terms of the GNU General Public License.
+# ----------------------------------------------------------------------
+
+cf1='IKCFG_ST\037\213\010'
+cf2='0123456789'
+
+dump_config()
+{
+	if	pos=`tr "$cf1\n$cf2" "\n$cf2=" < "$1" | grep -abo "^$cf2"`
+	then
+		pos=${pos%%:*}
+		tail -c+$(($pos+8)) "$1" | zcat > $tmp1 2> /dev/null
+		if	[ $? != 1 ]
+		then	# exit status must be 0 or 2 (trailing garbage warning)
+			cat $tmp1
+			exit 0
+		fi
+	fi
+}
+
+try_decompress()
+{
+	for	pos in `tr "$1\n$2" "\n$2=" < "$img" | grep -abo "^$2"`
+	do
+		pos=${pos%%:*}
+		tail -c+$pos "$img" | $3 > $tmp2 2> /dev/null
+		dump_config $tmp2
+	done
+}
+
+# Check invocation:
+me=${0##*/}
+img=$1
+if	[ $# -ne 1 -o ! -s "$img" ]
+then
+	echo "Usage: $me <kernel-image>" >&2
+	exit 2
+fi
+
+# Prepare temp files:
+tmp1=/tmp/ikconfig$$.1
+tmp2=/tmp/ikconfig$$.2
+trap "rm -f $tmp1 $tmp2" 0
+
+# Initial attempt for uncompressed images or objects:
+dump_config "$img"
+
+# That didn't work, so retry after decompression.
+try_decompress '\037\213\010' xy    gunzip
+try_decompress '\3757zXZ\000' abcde unxz
+try_decompress 'BZh'          xy    bunzip2
+try_decompress '\135\0\0\0'   xxx   unlzma
+try_decompress '\211\114\132' xy    'lzop -d'
+try_decompress '\002\041\114\030' xyy 'lz4 -d -l'
+try_decompress '\050\265\057\375' xxx unzstd
+
+# Bail out:
+echo "$me: Cannot find kernel config." >&2
+exit 1