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, 64 insertions, 0 deletions

diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
new file mode 100644
index 000000000..2dba7f83e
--- /dev/null
+++ b/arch/x86/lib/Makefile
@@ -0,0 +1,64 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for x86 specific library files.
+#
+
+# Produces uninteresting flaky coverage.
+KCOV_INSTRUMENT_delay.o	:= n
+
+# KCSAN uses udelay for introducing watchpoint delay; avoid recursion.
+KCSAN_SANITIZE_delay.o := n
+ifdef CONFIG_KCSAN
+# In case KCSAN+lockdep+ftrace are enabled, disable ftrace for delay.o to avoid
+# lockdep -> [other libs] -> KCSAN -> udelay -> ftrace -> lockdep recursion.
+CFLAGS_REMOVE_delay.o = $(CC_FLAGS_FTRACE)
+endif
+
+inat_tables_script = $(srctree)/arch/x86/tools/gen-insn-attr-x86.awk
+inat_tables_maps = $(srctree)/arch/x86/lib/x86-opcode-map.txt
+quiet_cmd_inat_tables = GEN     $@
+      cmd_inat_tables = $(AWK) -f $(inat_tables_script) $(inat_tables_maps) > $@
+
+$(obj)/inat-tables.c: $(inat_tables_script) $(inat_tables_maps)
+	$(call cmd,inat_tables)
+
+$(obj)/inat.o: $(obj)/inat-tables.c
+
+clean-files := inat-tables.c
+
+obj-$(CONFIG_SMP) += msr-smp.o cache-smp.o
+
+lib-y := delay.o misc.o cmdline.o cpu.o
+lib-y += usercopy_$(BITS).o usercopy.o getuser.o putuser.o
+lib-y += memcpy_$(BITS).o
+lib-y += pc-conf-reg.o
+lib-$(CONFIG_ARCH_HAS_COPY_MC) += copy_mc.o copy_mc_64.o
+lib-$(CONFIG_INSTRUCTION_DECODER) += insn.o inat.o insn-eval.o
+lib-$(CONFIG_RANDOMIZE_BASE) += kaslr.o
+lib-$(CONFIG_FUNCTION_ERROR_INJECTION)	+= error-inject.o
+lib-$(CONFIG_MITIGATION_RETPOLINE) += retpoline.o
+
+obj-y += msr.o msr-reg.o msr-reg-export.o hweight.o
+obj-y += iomem.o
+
+ifeq ($(CONFIG_X86_32),y)
+        obj-y += atomic64_32.o
+        lib-y += atomic64_cx8_32.o
+        lib-y += checksum_32.o
+        lib-y += strstr_32.o
+        lib-y += string_32.o
+        lib-y += memmove_32.o
+        lib-y += cmpxchg8b_emu.o
+ifneq ($(CONFIG_X86_CX8),y)
+        lib-y += atomic64_386_32.o
+endif
+else
+ifneq ($(CONFIG_GENERIC_CSUM),y)
+        lib-y += csum-partial_64.o csum-copy_64.o csum-wrappers_64.o
+endif
+        lib-y += clear_page_64.o copy_page_64.o
+        lib-y += memmove_64.o memset_64.o
+        lib-y += copy_user_64.o copy_user_uncached_64.o
+        lib-y += cmpxchg16b_emu.o
+        lib-y += bhi.o
+endif