s390/alternatives: Allow early alternative patching in decompressor

Add the required code to patch alternatives early in the decompressor.
This is required for the upcoming lowcore relocation changes, where
alternatives for facility 193 need to get patched before lowcore
alternatives.
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Co-developed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/boot/Makefile

@@ -39,7 +39,7 @@ CFLAGS_sclp_early_core.o += -I$(srctree)/drivers/s390/char
 
 obj-y	:= head.o als.o startup.o physmem_info.o ipl_parm.o ipl_report.o vmem.o
 obj-y	+= string.o ebcdic.o sclp_early_core.o mem.o ipl_vmparm.o cmdline.o
-obj-y	+= version.o pgm_check_info.o ctype.o ipl_data.o relocs.o
+obj-y	+= version.o pgm_check_info.o ctype.o ipl_data.o relocs.o alternative.o
 obj-$(findstring y, $(CONFIG_PROTECTED_VIRTUALIZATION_GUEST) $(CONFIG_PGSTE))	+= uv.o
 obj-$(CONFIG_RANDOMIZE_BASE)	+= kaslr.o
 obj-y	+= $(if $(CONFIG_KERNEL_UNCOMPRESSED),,decompressor.o) info.o

arch/s390/boot/alternative.c

+// SPDX-License-Identifier: GPL-2.0
+
+#include "../kernel/alternative.c"

arch/s390/boot/boot.h

@@ -30,6 +30,8 @@ struct vmlinux_info {
 	unsigned long init_mm_off;
 	unsigned long swapper_pg_dir_off;
 	unsigned long invalid_pg_dir_off;
+	unsigned long alt_instructions;
+	unsigned long alt_instructions_end;
 #ifdef CONFIG_KASAN
 	unsigned long kasan_early_shadow_page_off;
 	unsigned long kasan_early_shadow_pte_off;

arch/s390/boot/startup.c

@@ -376,6 +376,8 @@ static void kaslr_adjust_vmlinux_info(long offset)
 	vmlinux.init_mm_off += offset;
 	vmlinux.swapper_pg_dir_off += offset;
 	vmlinux.invalid_pg_dir_off += offset;
+	vmlinux.alt_instructions += offset;
+	vmlinux.alt_instructions_end += offset;
 #ifdef CONFIG_KASAN
 	vmlinux.kasan_early_shadow_page_off += offset;
 	vmlinux.kasan_early_shadow_pte_off += offset;
@@ -507,6 +509,9 @@ void startup_kernel(void)
 	kaslr_adjust_got(__kaslr_offset);
 	setup_vmem(__kaslr_offset, __kaslr_offset + kernel_size, asce_limit);
 	copy_bootdata();
+	__apply_alternatives((struct alt_instr *)_vmlinux_info.alt_instructions,
+			     (struct alt_instr *)_vmlinux_info.alt_instructions_end,
+			     ALT_CTX_EARLY);
 
 	/*
 	 * Save KASLR offset for early dumps, before vmcore_info is set.

arch/s390/include/asm/alternative.h

@@ -27,15 +27,21 @@
  * alternative should be applied.
  */
 
-#define ALT_CTX_LATE		1
-#define ALT_CTX_ALL		ALT_CTX_LATE
+#define ALT_CTX_EARLY		1
+#define ALT_CTX_LATE		2
+#define ALT_CTX_ALL		(ALT_CTX_EARLY | ALT_CTX_LATE)
 
-#define ALT_TYPE_FACILITY	0
+#define ALT_TYPE_FACILITY_EARLY	0
+#define ALT_TYPE_FACILITY	1
 
 #define ALT_DATA_SHIFT		0
 #define ALT_TYPE_SHIFT		20
 #define ALT_CTX_SHIFT		28
 
+#define ALT_FACILITY_EARLY(facility)	(ALT_CTX_EARLY << ALT_CTX_SHIFT		   | \
+					 ALT_TYPE_FACILITY_EARLY << ALT_TYPE_SHIFT | \
+					 (facility) << ALT_DATA_SHIFT)
+
 #define ALT_FACILITY(facility)		(ALT_CTX_LATE << ALT_CTX_SHIFT		| \
 					 ALT_TYPE_FACILITY << ALT_TYPE_SHIFT	| \
 					 (facility) << ALT_DATA_SHIFT)

arch/s390/kernel/alternative.c

@@ -18,9 +18,14 @@ void __apply_alternatives(struct alt_instr *start, struct alt_instr *end, unsign
 		if (!(a->ctx & ctx))
 			continue;
 		switch (a->type) {
+		case ALT_TYPE_FACILITY_EARLY:
+			replace = test_facility(a->data);
+			break;
+#ifndef __DECOMPRESSOR
 		case ALT_TYPE_FACILITY:
 			replace = __test_facility(a->data, alt_stfle_fac_list);
 			break;
+#endif
 		default:
 			replace = false;
 		}

arch/s390/kernel/vmlinux.lds.S

@@ -222,6 +222,8 @@ SECTIONS
 		QUAD(init_mm)
 		QUAD(swapper_pg_dir)
 		QUAD(invalid_pg_dir)
+		QUAD(__alt_instructions)
+		QUAD(__alt_instructions_end)
 #ifdef CONFIG_KASAN
 		QUAD(kasan_early_shadow_page)
 		QUAD(kasan_early_shadow_pte)