arm64: mm: fold alternatives into .init

Currently we treat the alternatives separately from other data that's
only used during initialisation, using separate .altinstructions and
.altinstr_replacement linker sections. These are freed for general
allocation separately from .init*. This is problematic as:

* We do not remove execute permissions, as we do for .init, leaving the
memory executable.

* We pad between them, making the kernel Image bianry up to PAGE_SIZE
bytes larger than necessary.

This patch moves the two sections into the contiguous region used for
.init*. This saves some memory, ensures that we remove execute
permissions, and allows us to remove some code made redundant by this
reorganisation.

Signed-off-by: Mark Rutland <[e-mail]>
Cc: Andre Przywara <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: Jeremy Linton <[e-mail]>
Cc: Laura Abbott <[e-mail]>
Cc: Will Deacon <[e-mail]>
Signed-off-by: Will Deacon <[e-mail]>

arch/arm64/include/asm/alternative.h

···
 
 void __init apply_alternatives_all(void);
 void apply_alternatives(void *start, size_t length);
-void free_alternatives_memory(void);
 
 #define ALTINSTR_ENTRY(feature)						      \
 	" .word 661b - .\n"				/* label           */ \

arch/arm64/kernel/alternative.c

···
 
 	__apply_alternatives(&region);
 }
-
-void free_alternatives_memory(void)
-{
-	free_reserved_area(__alt_instructions, __alt_instructions_end,
-			   0, "alternatives");
-}

arch/arm64/kernel/vmlinux.lds.S

···
 
 	PERCPU_SECTION(64)
 
-	. = ALIGN(PAGE_SIZE);
-	__init_end = .;
-
 	. = ALIGN(4);
 	.altinstructions : {
 		__alt_instructions = .;
···
 	}
 
 	. = ALIGN(PAGE_SIZE);
+	__init_end = .;
+
 	_data = .;
 	_sdata = .;
 	RW_DATA_SECTION(64, PAGE_SIZE, THREAD_SIZE)

arch/arm64/mm/init.c

···
 {
 	fixup_init();
 	free_initmem_default(0);
-	free_alternatives_memory();
 }
 
 #ifdef CONFIG_BLK_DEV_INITRD