s390/boot: make stacks part of the decompressor's image

Instead of using constant addresses for the normal and dump-info stacks,
allocate both stacks in the decompressor's image and load the stack register
in a position-independent manner.

This will allow loading and entering the decompressor at an arbitrary
memory address without corrupting the content at the fixed addresses
used until now for both stacks. This is one of the prerequisites
for being able to kexec the decompressor from its load address without
relocating it first.
Signed-off-by: Alexander Egorenkov <egorenar@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/boot/boot.h

@@ -2,13 +2,8 @@
 #ifndef BOOT_BOOT_H
 #define BOOT_BOOT_H
 
-#include <linux/types.h>
-
-#define BOOT_STACK_OFFSET 0x8000
-
-#ifndef __ASSEMBLY__
-
 #include <asm/extable.h>
+#include <linux/types.h>
 
 void startup_kernel(void);
 unsigned long detect_memory(void);
@@ -35,8 +30,8 @@ extern char _stext_dma[], _etext_dma[];
 extern struct exception_table_entry _start_dma_ex_table[];
 extern struct exception_table_entry _stop_dma_ex_table[];
 extern char _decompressor_syms_start[], _decompressor_syms_end[];
+extern char _stack_start[], _stack_end[];
 
 unsigned long read_ipl_report(unsigned long safe_offset);
 
-#endif /* __ASSEMBLY__ */
 #endif /* BOOT_BOOT_H */

arch/s390/boot/compressed/vmlinux.lds.S

 /* SPDX-License-Identifier: GPL-2.0 */
 #include <asm-generic/vmlinux.lds.h>
 #include <asm/vmlinux.lds.h>
+#include <asm/thread_info.h>
+#include <asm/page.h>
 
 OUTPUT_FORMAT("elf64-s390", "elf64-s390", "elf64-s390")
 OUTPUT_ARCH(s390:64-bit)
@@ -69,6 +71,17 @@ SECTIONS
 		*(.bss)
 		*(.bss.*)
 		*(COMMON)
+		/*
+		 * Stacks for the decompressor
+		 */
+		. = ALIGN(PAGE_SIZE);
+		_dump_info_stack_start = .;
+		. += PAGE_SIZE;
+		_dump_info_stack_end = .;
+		. = ALIGN(PAGE_SIZE);
+		_stack_start = .;
+		. += BOOT_STACK_SIZE;
+		_stack_end = .;
 		_ebss = .;
 	}
 

arch/s390/boot/head.S

@@ -25,10 +25,8 @@
 #include <linux/init.h>
 #include <linux/linkage.h>
 #include <asm/asm-offsets.h>
-#include <asm/thread_info.h>
 #include <asm/page.h>
 #include <asm/ptrace.h>
-#include "boot.h"
 
 #define ARCH_OFFSET	4
 
@@ -320,13 +318,11 @@ SYM_CODE_START_LOCAL(startup_normal)
 	mvc	__LC_LAST_UPDATE_CLOCK(8),__LC_BOOT_CLOCK+1
 	spt	6f-.LPG0(%r13)
 	mvc	__LC_LAST_UPDATE_TIMER(8),6f-.LPG0(%r13)
-	l	%r15,.Lstack-.LPG0(%r13)
+	larl	%r15,_stack_end-STACK_FRAME_OVERHEAD
 	brasl	%r14,verify_facilities
 	brasl	%r14,startup_kernel
 SYM_CODE_END(startup_normal)
 
-.Lstack:
-	.long	BOOT_STACK_OFFSET + BOOT_STACK_SIZE - STACK_FRAME_OVERHEAD
 	.align	8
 6:	.long	0x7fffffff,0xffffffff
 .Lext_new_psw:
@@ -386,15 +382,13 @@ SYM_CODE_START_LOCAL(startup_pgm_check_handler)
 	oi	__LC_RETURN_PSW+1,0x2	# set wait state bit
 	larl	%r9,.Lold_psw_disabled_wait
 	stg	%r9,__LC_PGM_NEW_PSW+8
-	l	%r15,.Ldump_info_stack-.Lold_psw_disabled_wait(%r9)
+	larl	%r15,_dump_info_stack_end-STACK_FRAME_OVERHEAD
 	brasl	%r14,print_pgm_check_info
 .Lold_psw_disabled_wait:
 	la	%r8,4095
 	lmg	%r0,%r15,__LC_GPREGS_SAVE_AREA-4095(%r8)
 	lpswe	__LC_RETURN_PSW		# disabled wait
 SYM_CODE_END(startup_pgm_check_handler)
-.Ldump_info_stack:
-	.long	0x5000 + PAGE_SIZE - STACK_FRAME_OVERHEAD
 
 #
 # params at 10400 (setup.h)

arch/s390/boot/pgm_check_info.c

@@ -125,8 +125,8 @@ void decompressor_printk(const char *fmt, ...)
 
 static noinline void print_stacktrace(void)
 {
-	struct stack_info boot_stack = { STACK_TYPE_TASK, BOOT_STACK_OFFSET,
-					 BOOT_STACK_OFFSET + BOOT_STACK_SIZE };
+	struct stack_info boot_stack = { STACK_TYPE_TASK, (unsigned long)_stack_start,
+					 (unsigned long)_stack_end };
 	unsigned long sp = S390_lowcore.gpregs_save_area[15];
 	bool first = true;