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, 98 insertions, 0 deletions

diff --git a/tools/docs/features-refresh.sh b/tools/docs/features-refresh.sh
new file mode 100755
index 000000000..c2288124e
--- /dev/null
+++ b/tools/docs/features-refresh.sh
@@ -0,0 +1,98 @@
+#
+# Small script that refreshes the kernel feature support status in place.
+#
+
+for F_FILE in Documentation/features/*/*/arch-support.txt; do
+	F=$(grep "^#         Kconfig:" "$F_FILE" | cut -c26-)
+
+	#
+	# Each feature F is identified by a pair (O, K), where 'O' can
+	# be either the empty string (for 'nop') or "not" (the logical
+	# negation operator '!'); other operators are not supported.
+	#
+	O=""
+	K=$F
+	if [[ "$F" == !* ]]; then
+		O="not"
+		K=$(echo $F | sed -e 's/^!//g')
+	fi
+
+	#
+	# F := (O, K) is 'valid' iff there is a Kconfig file (for some
+	# arch) which contains K.
+	#
+	# Notice that this definition entails an 'asymmetry' between
+	# the case 'O = ""' and the case 'O = "not"'. E.g., F may be
+	# _invalid_ if:
+	#
+	# [case 'O = ""']
+	#   1) no arch provides support for F,
+	#   2) K does not exist (e.g., it was renamed/mis-typed);
+	#
+	# [case 'O = "not"']
+	#   3) all archs provide support for F,
+	#   4) as in (2).
+	#
+	# The rationale for adopting this definition (and, thus, for
+	# keeping the asymmetry) is:
+	#
+	#       We want to be able to 'detect' (2) (or (4)).
+	#
+	# (1) and (3) may further warn the developers about the fact
+	# that K can be removed.
+	#
+	F_VALID="false"
+	for ARCH_DIR in arch/*/; do
+		K_FILES=$(find $ARCH_DIR -name "Kconfig*")
+		K_GREP=$(grep "$K" $K_FILES)
+		if [ ! -z "$K_GREP" ]; then
+			F_VALID="true"
+			break
+		fi
+	done
+	if [ "$F_VALID" = "false" ]; then
+		printf "WARNING: '%s' is not a valid Kconfig\n" "$F"
+	fi
+
+	T_FILE="$F_FILE.tmp"
+	grep "^#" $F_FILE > $T_FILE
+	echo "    -----------------------" >> $T_FILE
+	echo "    |         arch |status|" >> $T_FILE
+	echo "    -----------------------" >> $T_FILE
+	for ARCH_DIR in arch/*/; do
+		ARCH=$(echo $ARCH_DIR | sed -e 's/^arch//g' | sed -e 's/\///g')
+		K_FILES=$(find $ARCH_DIR -name "Kconfig*")
+		K_GREP=$(grep "$K" $K_FILES)
+		#
+		# Arch support status values for (O, K) are updated according
+		# to the following rules.
+		#
+		#   - ("", K) is 'supported by a given arch', if there is a
+		#     Kconfig file for that arch which contains K;
+		#
+		#   - ("not", K) is 'supported by a given arch', if there is
+		#     no Kconfig file for that arch which contains K;
+		#
+		#   - otherwise: preserve the previous status value (if any),
+		#                default to 'not yet supported'.
+		#
+		# Notice that, according these rules, invalid features may be
+		# updated/modified.
+		#
+		if [ "$O" = "" ] && [ ! -z "$K_GREP" ]; then
+			printf "    |%12s: |  ok  |\n" "$ARCH" >> $T_FILE
+		elif [ "$O" = "not" ] && [ -z "$K_GREP" ]; then
+			printf "    |%12s: |  ok  |\n" "$ARCH" >> $T_FILE
+		else
+			S=$(grep -v "^#" "$F_FILE" | grep " $ARCH:")
+			if [ ! -z "$S" ]; then
+				echo "$S" >> $T_FILE
+			else
+				printf "    |%12s: | TODO |\n" "$ARCH" \
+					>> $T_FILE
+			fi
+		fi
+	done
+	echo "    -----------------------" >> $T_FILE
+	mv $T_FILE $F_FILE
+done