x86: Handle KCOV __init vs inline mismatches

GCC appears to have kind of fragile inlining heuristics, in the
sense that it can change whether or not it inlines something based on
optimizations. It looks like the kcov instrumentation being added (or in
this case, removed) from a function changes the optimization results,
and some functions marked "inline" are _not_ inlined. In that case,
we end up with __init code calling a function not marked __init, and we
get the build warnings I'm trying to eliminate in the coming patch that
adds __no_sanitize_coverage to __init functions:

WARNING: modpost: vmlinux: section mismatch in reference: xbc_exit+0x8 (section: .text.unlikely) -> _xbc_exit (section: .init.text)
WARNING: modpost: vmlinux: section mismatch in reference: real_mode_size_needed+0x15 (section: .text.unlikely) -> real_mode_blob_end (section: .init.data)
WARNING: modpost: vmlinux: section mismatch in reference: __set_percpu_decrypted+0x16 (section: .text.unlikely) -> early_set_memory_decrypted (section: .init.text)
WARNING: modpost: vmlinux: section mismatch in reference: memblock_alloc_from+0x26 (section: .text.unlikely) -> memblock_alloc_try_nid (section: .init.text)
WARNING: modpost: vmlinux: section mismatch in reference: acpi_arch_set_root_pointer+0xc (section: .text.unlikely) -> x86_init (section: .init.data)
WARNING: modpost: vmlinux: section mismatch in reference: acpi_arch_get_root_pointer+0x8 (section: .text.unlikely) -> x86_init (section: .init.data)
WARNING: modpost: vmlinux: section mismatch in reference: efi_config_table_is_usable+0x16 (section: .text.unlikely) -> xen_efi_config_table_is_usable (section: .init.text)

This problem is somewhat fragile (though using either __always_inline
or __init will deterministically solve it), but we've tripped over
this before with GCC and the solution has usually been to just use
__always_inline and move on.

For x86 this means forcing several functions to be inline with
__always_inline.

Link: https://lore.kernel.org/r/20250724055029.3623499-2-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>

arch/x86/include/asm/acpi.h

@@ -158,13 +158,13 @@ static inline bool acpi_has_cpu_in_madt(void)
 }
 
 #define ACPI_HAVE_ARCH_SET_ROOT_POINTER
-static inline void acpi_arch_set_root_pointer(u64 addr)
+static __always_inline void acpi_arch_set_root_pointer(u64 addr)
 {
 	x86_init.acpi.set_root_pointer(addr);
 }
 
 #define ACPI_HAVE_ARCH_GET_ROOT_POINTER
-static inline u64 acpi_arch_get_root_pointer(void)
+static __always_inline u64 acpi_arch_get_root_pointer(void)
 {
 	return x86_init.acpi.get_root_pointer();
 }

arch/x86/include/asm/realmode.h

@@ -78,7 +78,7 @@ extern unsigned char secondary_startup_64[];
 extern unsigned char secondary_startup_64_no_verify[];
 #endif
 
-static inline size_t real_mode_size_needed(void)
+static __always_inline size_t real_mode_size_needed(void)
 {
 	if (real_mode_header)
 		return 0;	/* already allocated. */

arch/x86/kernel/kvm.c

@@ -420,7 +420,7 @@ static u64 kvm_steal_clock(int cpu)
 	return steal;
 }
 
-static inline void __set_percpu_decrypted(void *ptr, unsigned long size)
+static inline __init void __set_percpu_decrypted(void *ptr, unsigned long size)
 {
 	early_set_memory_decrypted((unsigned long) ptr, size);
 }

arch/x86/mm/init_64.c

@@ -806,7 +806,7 @@ kernel_physical_mapping_change(unsigned long paddr_start,
 }
 
 #ifndef CONFIG_NUMA
-static inline void x86_numa_init(void)
+static __always_inline void x86_numa_init(void)
 {
 	memblock_set_node(0, PHYS_ADDR_MAX, &memblock.memory, 0);
 }

include/linux/acpi.h

@@ -759,13 +759,13 @@ int acpi_arch_timer_mem_init(struct arch_timer_mem *timer_mem, int *timer_count)
 #endif
 
 #ifndef ACPI_HAVE_ARCH_SET_ROOT_POINTER
-static inline void acpi_arch_set_root_pointer(u64 addr)
+static __always_inline void acpi_arch_set_root_pointer(u64 addr)
 {
 }
 #endif
 
 #ifndef ACPI_HAVE_ARCH_GET_ROOT_POINTER
-static inline u64 acpi_arch_get_root_pointer(void)
+static __always_inline u64 acpi_arch_get_root_pointer(void)
 {
 	return 0;
 }

include/linux/bootconfig.h

@@ -290,7 +290,7 @@ int __init xbc_get_info(int *node_size, size_t *data_size);
 /* XBC cleanup data structures */
 void __init _xbc_exit(bool early);
 
-static inline void xbc_exit(void)
+static __always_inline void xbc_exit(void)
 {
 	_xbc_exit(false);
 }

include/linux/efi.h

@@ -1334,7 +1334,7 @@ struct linux_efi_initrd {
 
 bool xen_efi_config_table_is_usable(const efi_guid_t *guid, unsigned long table);
 
-static inline
+static __always_inline
 bool efi_config_table_is_usable(const efi_guid_t *guid, unsigned long table)
 {
 	if (!IS_ENABLED(CONFIG_XEN_EFI))

include/linux/memblock.h

@@ -463,7 +463,7 @@ static inline void *memblock_alloc_raw(phys_addr_t size,
 					  NUMA_NO_NODE);
 }
 
-static inline void *memblock_alloc_from(phys_addr_t size,
+static __always_inline void *memblock_alloc_from(phys_addr_t size,
 						phys_addr_t align,
 						phys_addr_t min_addr)
 {

include/linux/smp.h

@@ -221,7 +221,7 @@ static inline void wake_up_all_idle_cpus(void) {  }
 
 #ifdef CONFIG_UP_LATE_INIT
 extern void __init up_late_init(void);
-static inline void smp_init(void) { up_late_init(); }
+static __always_inline void smp_init(void) { up_late_init(); }
 #else
 static inline void smp_init(void) { }
 #endif

kernel/kexec_handover.c

@@ -305,8 +305,8 @@ err_free:
 	return -ENOMEM;
 }
 
-static void deserialize_bitmap(unsigned int order,
-			       struct khoser_mem_bitmap_ptr *elm)
+static void __init deserialize_bitmap(unsigned int order,
+				      struct khoser_mem_bitmap_ptr *elm)
 {
 	struct kho_mem_phys_bits *bitmap = KHOSER_LOAD_PTR(elm->bitmap);
 	unsigned long bit;