Merge tag 'x86-build-2025-05-25' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 build updates from Ingo Molnar:
 "Add the CONFIG_X86_NATIVE_CPU=y build option to locally optimize the
  kernel build with '-march=native'"

* tag 'x86-build-2025-05-25' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/kbuild/64: Restrict clang versions that can use '-march=native'
  x86/kbuild/64: Test for the availability of the -mtune=native compiler flag
  x86/kbuild/64: Add the CONFIG_X86_NATIVE_CPU option to locally optimize the kernel with '-march=native'

Author: torvalds

arch/x86/Kconfig.cpu

@@ -245,6 +245,30 @@ config MATOM
 
 endchoice
 
+config CC_HAS_MARCH_NATIVE
+	# This flag might not be available in cross-compilers:
+	def_bool $(cc-option, -march=native)
+	# LLVM 18 has an easily triggered internal compiler error in core
+	# networking code with '-march=native' on certain systems:
+	# https://github.com/llvm/llvm-project/issues/72026
+	# LLVM 19 introduces an optimization that resolves some high stack
+	# usage warnings that only appear wth '-march=native'.
+	depends on CC_IS_GCC || CLANG_VERSION >= 190100
+
+config X86_NATIVE_CPU
+	bool "Build and optimize for local/native CPU"
+	depends on X86_64
+	depends on CC_HAS_MARCH_NATIVE
+	help
+	  Optimize for the current CPU used to compile the kernel.
+	  Use this option if you intend to build the kernel for your
+	  local machine.
+
+	  Note that such a kernel might not work optimally on a
+	  different x86 machine.
+
+	  If unsure, say N.
+
 config X86_GENERIC
 	bool "Generic x86 support"
 	depends on X86_32

arch/x86/Makefile

@@ -173,8 +173,13 @@ else
 	# Use -mskip-rax-setup if supported.
 	KBUILD_CFLAGS += $(call cc-option,-mskip-rax-setup)
 
+ifdef CONFIG_X86_NATIVE_CPU
+        KBUILD_CFLAGS += -march=native
+        KBUILD_RUSTFLAGS += -Ctarget-cpu=native
+else
         KBUILD_CFLAGS += -march=x86-64 -mtune=generic
         KBUILD_RUSTFLAGS += -Ctarget-cpu=x86-64 -Ztune-cpu=generic
+endif
 
         KBUILD_CFLAGS += -mno-red-zone
         KBUILD_CFLAGS += -mcmodel=kernel