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, 153 insertions, 0 deletions

diff --git a/scripts/Makefile.dtbs b/scripts/Makefile.dtbs
new file mode 100644
index 000000000..c4e466390
--- /dev/null
+++ b/scripts/Makefile.dtbs
@@ -0,0 +1,153 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+all-dtb := $(dtb-y) $(dtb-)
+
+# If CONFIG_OF_ALL_DTBS is enabled, all DT blobs are built
+dtb-$(CONFIG_OF_ALL_DTBS) += $(dtb-)
+
+# Composite DTB (i.e. DTB constructed by overlay)
+multi-dtb-y := $(call multi-search, $(dtb-y), .dtb, -dtbs)
+# Primitive DTB compiled from *.dts
+real-dtb-y := $(call real-search, $(dtb-y), .dtb, -dtbs)
+# Base DTB that overlay is applied onto
+base-dtb-y := $(filter %.dtb, $(call real-search, $(multi-dtb-y), .dtb, -dtbs))
+
+# Ensure that any .dtbo is applied to at least one base .dtb. Otherwise, it
+# does not get validated.
+applied-dtbo := $(filter %.dtbo, \
+	$(call real-search, $(call multi-search, $(all-dtb), .dtb, -dtbs), .dtb, -dtbs))
+unapplied-dtbo := $(filter-out $(applied-dtbo),$(filter %.dtbo, $(dtb-y)))
+$(if $(unapplied-dtbo), $(warning .dtbo is not applied to any base: $(unapplied-dtbo)))
+
+dtb-y           := $(addprefix $(obj)/, $(dtb-y))
+multi-dtb-y     := $(addprefix $(obj)/, $(multi-dtb-y))
+real-dtb-y      := $(addprefix $(obj)/, $(real-dtb-y))
+
+always-y        += $(dtb-y)
+targets         += $(real-dtb-y)
+
+# dtbs-list
+# ---------------------------------------------------------------------------
+
+ifdef need-dtbslist
+subdir-dtbslist := $(addsuffix /dtbs-list, $(subdir-ym))
+dtb-y           += $(subdir-dtbslist)
+always-y        += $(obj)/dtbs-list
+endif
+
+$(subdir-dtbslist): $(obj)/%/dtbs-list: $(obj)/% ;
+
+$(obj)/dtbs-list: $(dtb-y) FORCE
+	$(call if_changed,gen_order)
+
+# Assembly file to wrap dtb(o)
+# ---------------------------------------------------------------------------
+
+builtin-dtb-section = $(if $(filter arch/$(SRCARCH)/boot/dts%, $(obj)),.dtb.init.rodata,.rodata)
+
+# Generate an assembly file to wrap the output of the device tree compiler
+quiet_cmd_wrap_S_dtb = WRAP    $@
+      cmd_wrap_S_dtb = {								\
+		symbase=__$(patsubst .%,%,$(suffix $<))_$(subst -,_,$(notdir $*));	\
+		echo '\#include <asm-generic/vmlinux.lds.h>';				\
+		echo '.section $(builtin-dtb-section),"a"';				\
+		echo '.balign STRUCT_ALIGNMENT';					\
+		echo ".global $${symbase}_begin";					\
+		echo "$${symbase}_begin:";						\
+		echo '.incbin "$<" ';							\
+		echo ".global $${symbase}_end";						\
+		echo "$${symbase}_end:";						\
+		echo '.balign STRUCT_ALIGNMENT';					\
+	} > $@
+
+$(obj)/%.dtb.S: $(obj)/%.dtb FORCE
+	$(call if_changed,wrap_S_dtb)
+
+$(obj)/%.dtbo.S: $(obj)/%.dtbo FORCE
+	$(call if_changed,wrap_S_dtb)
+
+# Schema check
+# ---------------------------------------------------------------------------
+
+ifneq ($(CHECK_DTBS),)
+DT_CHECKER ?= dt-validate
+DT_CHECKER_FLAGS ?= $(if $(DT_SCHEMA_FILES),-l $(DT_SCHEMA_FILES),-m)
+DT_BINDING_DIR := Documentation/devicetree/bindings
+DT_TMP_SCHEMA := $(objtree)/$(DT_BINDING_DIR)/processed-schema.json
+dtb-check-enabled = $(if $(filter %.dtb, $@),y)
+endif
+
+quiet_dtb_check_tag = $(if $(dtb-check-enabled),[C],   )
+cmd_dtb_check = $(if $(dtb-check-enabled),; $(DT_CHECKER) $(DT_CHECKER_FLAGS) -u $(srctree)/$(DT_BINDING_DIR) -p $(DT_TMP_SCHEMA) $@ || true)
+
+# Overlay
+# ---------------------------------------------------------------------------
+
+# NOTE:
+# Do not replace $(filter %.dtb %.dtbo, $^) with $(real-prereqs). When a single
+# DTB is turned into a multi-blob DTB, $^ will contain header file dependencies
+# recorded in the .*.cmd file.
+quiet_cmd_fdtoverlay = OVL $(quiet_dtb_check_tag) $@
+      cmd_fdtoverlay = $(objtree)/scripts/dtc/fdtoverlay -o $@ -i $(filter %.dtb %.dtbo, $^) $(cmd_dtb_check)
+
+$(multi-dtb-y): $(DT_TMP_SCHEMA) FORCE
+	$(call if_changed,fdtoverlay)
+$(call multi_depend, $(multi-dtb-y), .dtb, -dtbs)
+
+# DTC
+# ---------------------------------------------------------------------------
+
+DTC ?= $(objtree)/scripts/dtc/dtc
+DTC_FLAGS += -Wno-unique_unit_address
+
+# Disable noisy checks by default
+ifeq ($(findstring 1,$(KBUILD_EXTRA_WARN)),)
+DTC_FLAGS += -Wno-unit_address_vs_reg \
+             -Wno-avoid_unnecessary_addr_size \
+             -Wno-alias_paths \
+             -Wno-interrupt_map \
+             -Wno-simple_bus_reg
+else
+DTC_FLAGS += -Wunique_unit_address_if_enabled
+endif
+
+ifneq ($(findstring 2,$(KBUILD_EXTRA_WARN)),)
+DTC_FLAGS += -Wnode_name_chars_strict \
+             -Wproperty_name_chars_strict \
+             -Wunique_unit_address
+endif
+
+DTC_FLAGS += $(DTC_FLAGS_$(target-stem))
+
+# Set -@ if the target is a base DTB that overlay is applied onto
+DTC_FLAGS += $(if $(filter $(patsubst $(obj)/%,%,$@), $(base-dtb-y)), -@)
+
+DTC_INCLUDE := $(srctree)/scripts/dtc/include-prefixes
+
+dtc_cpp_flags = -Wp,-MMD,$(depfile).pre.tmp -nostdinc -I $(DTC_INCLUDE) -undef -D__DTS__
+
+dtc-tmp = $(subst $(comma),_,$(dot-target).dts.tmp)
+
+quiet_cmd_dtc = DTC $(quiet_dtb_check_tag) $@
+      cmd_dtc = \
+	$(HOSTCC) -E $(dtc_cpp_flags) -x assembler-with-cpp -o $(dtc-tmp) $< ; \
+	$(DTC) -o $@ -b 0 $(addprefix -i,$(dir $<) $(DTC_INCLUDE)) \
+	       $(DTC_FLAGS) -d $(depfile).dtc.tmp $(dtc-tmp) ; \
+	cat $(depfile).pre.tmp $(depfile).dtc.tmp > $(depfile) \
+	$(cmd_dtb_check)
+
+$(obj)/%.dtb: $(obj)/%.dts $(DTC) $(DT_TMP_SCHEMA) FORCE
+	$(call if_changed_dep,dtc)
+
+$(obj)/%.dtbo: $(src)/%.dtso $(DTC) FORCE
+	$(call if_changed_dep,dtc)
+
+# targets
+# ---------------------------------------------------------------------------
+
+targets += $(always-y)
+
+# %.dtb.o <- %.dtb.S <- %.dtb <- %.dts
+# %.dtbo.o <- %.dtbo.S <- %.dtbo <- %.dtso
+targets += $(call intermediate_targets, .dtb.o, .dtb.S .dtb) \
+           $(call intermediate_targets, .dtbo.o, .dtbo.S .dtbo)