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, 139 insertions, 0 deletions

diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
new file mode 100644
index 000000000..3f9fb3698
--- /dev/null
+++ b/arch/x86/boot/Makefile
@@ -0,0 +1,139 @@
+#
+# arch/x86/boot/Makefile
+#
+# This file is subject to the terms and conditions of the GNU General Public
+# License.  See the file "COPYING" in the main directory of this archive
+# for more details.
+#
+# Copyright (C) 1994 by Linus Torvalds
+# Changed by many, many contributors over the years.
+#
+
+# If you want to preset the SVGA mode, uncomment the next line and
+# set SVGA_MODE to whatever number you want.
+# Set it to -DSVGA_MODE=NORMAL_VGA if you just want the EGA/VGA mode.
+# The number is the same as you would ordinarily press at bootup.
+
+SVGA_MODE	:= -DSVGA_MODE=NORMAL_VGA
+
+targets		:= vmlinux.bin setup.bin setup.elf bzImage
+targets		+= fdimage fdimage144 fdimage288 image.iso hdimage
+subdir-		:= compressed
+
+setup-y		+= a20.o bioscall.o cmdline.o copy.o cpu.o cpuflags.o cpucheck.o
+setup-y		+= early_serial_console.o edd.o header.o main.o memory.o
+setup-y		+= pm.o pmjump.o printf.o regs.o string.o tty.o video.o
+setup-y		+= video-mode.o version.o
+setup-$(CONFIG_X86_APM_BOOT) += apm.o
+
+# The link order of the video-*.o modules can matter.  In particular,
+# video-vga.o *must* be listed first, followed by video-vesa.o.
+# Hardware-specific drivers should follow in the order they should be
+# probed, and video-bios.o should typically be last.
+setup-y		+= video-vga.o
+setup-y		+= video-vesa.o
+setup-y		+= video-bios.o
+
+targets		+= $(setup-y)
+hostprogs	+= mkcpustr
+
+HOST_EXTRACFLAGS += -I$(srctree)/tools/include \
+		    -include include/generated/autoconf.h \
+	            -D__EXPORTED_HEADERS__
+
+$(obj)/cpu.o: $(obj)/cpustr.h
+
+quiet_cmd_cpustr = CPUSTR  $@
+      cmd_cpustr = $(obj)/mkcpustr > $@
+$(obj)/cpustr.h: $(obj)/mkcpustr FORCE
+	$(call if_changed,cpustr)
+targets += cpustr.h
+
+# ---------------------------------------------------------------------------
+
+KBUILD_CFLAGS	:= $(REALMODE_CFLAGS) -D_SETUP
+KBUILD_AFLAGS	:= $(KBUILD_CFLAGS) -D__ASSEMBLY__
+KBUILD_CFLAGS	+= -fno-asynchronous-unwind-tables
+KBUILD_CFLAGS	+= $(CONFIG_CC_IMPLICIT_FALLTHROUGH)
+
+$(obj)/bzImage: asflags-y  := $(SVGA_MODE)
+
+quiet_cmd_image = BUILD   $@
+      cmd_image = (dd if=$< bs=4k conv=sync status=none; cat $(filter-out $<,$(real-prereqs))) >$@
+
+$(obj)/bzImage: $(obj)/setup.bin $(obj)/vmlinux.bin FORCE
+	$(call if_changed,image)
+	@$(kecho) 'Kernel: $@ is ready' ' (#'$(or $(KBUILD_BUILD_VERSION),`cat .version`)')'
+
+OBJCOPYFLAGS_vmlinux.bin := -O binary -R .note -R .comment -S
+$(obj)/vmlinux.bin: $(obj)/compressed/vmlinux FORCE
+	$(call if_changed,objcopy)
+
+SETUP_OBJS = $(addprefix $(obj)/,$(setup-y))
+
+sed-zoffset := -e 's/^\([0-9a-fA-F]*\) [a-zA-Z] \(startup_32\|efi.._stub_entry\|efi\(32\)\?_pe_entry\|input_data\|kernel_info\|_end\|_ehead\|_text\|_e\?data\|_e\?sbat\|z_.*\)$$/\#define ZO_\2 0x\1/p'
+
+quiet_cmd_zoffset = ZOFFSET $@
+      cmd_zoffset = $(NM) $< | sed -n $(sed-zoffset) > $@
+
+targets += zoffset.h
+$(obj)/zoffset.h: $(obj)/compressed/vmlinux FORCE
+	$(call if_changed,zoffset)
+
+
+AFLAGS_header.o += -I$(objtree)/$(obj)
+$(obj)/header.o: $(obj)/zoffset.h
+
+LDFLAGS_setup.elf	:= -m elf_i386 -z noexecstack -T
+$(obj)/setup.elf: $(src)/setup.ld $(SETUP_OBJS) FORCE
+	$(call if_changed,ld)
+
+OBJCOPYFLAGS_setup.bin	:= -O binary
+$(obj)/setup.bin: $(obj)/setup.elf FORCE
+	$(call if_changed,objcopy)
+
+$(obj)/compressed/vmlinux: FORCE
+	$(Q)$(MAKE) $(build)=$(obj)/compressed $@
+
+# Set this if you want to pass append arguments to the
+# bzdisk/fdimage/hdimage/isoimage kernel
+FDARGS =
+# Set this if you want one or more initrds included in the image
+FDINITRD =
+
+imgdeps = $(obj)/bzImage $(obj)/mtools.conf $(src)/genimage.sh
+
+$(obj)/mtools.conf: $(src)/mtools.conf.in
+	sed -e 's|@OBJ@|$(obj)|g' < $< > $@
+
+targets += mtools.conf
+
+# genimage.sh requires bash, but it also has a bunch of other
+# external dependencies.
+quiet_cmd_genimage = GENIMAGE $3
+      cmd_genimage = $(BASH) $(src)/genimage.sh $2 $3 $(obj)/bzImage \
+		$(obj)/mtools.conf '$(FDARGS)' $(FDINITRD)
+
+PHONY += bzdisk fdimage fdimage144 fdimage288 hdimage isoimage
+
+# This requires write access to /dev/fd0
+# All images require syslinux to be installed; hdimage also requires
+# EDK2/OVMF if the kernel is compiled with the EFI stub.
+bzdisk: $(imgdeps)
+	$(call cmd,genimage,bzdisk,/dev/fd0)
+
+fdimage fdimage144: $(imgdeps)
+	$(call cmd,genimage,fdimage144,$(obj)/fdimage)
+	@$(kecho) 'Kernel: $(obj)/fdimage is ready'
+
+fdimage288: $(imgdeps)
+	$(call cmd,genimage,fdimage288,$(obj)/fdimage)
+	@$(kecho) 'Kernel: $(obj)/fdimage is ready'
+
+hdimage: $(imgdeps)
+	$(call cmd,genimage,hdimage,$(obj)/hdimage)
+	@$(kecho) 'Kernel: $(obj)/hdimage is ready'
+
+isoimage: $(imgdeps)
+	$(call cmd,genimage,isoimage,$(obj)/image.iso)
+	@$(kecho) 'Kernel: $(obj)/image.iso is ready'