x86/fred: Fix init_task thread stack pointer initialization

As TOP_OF_KERNEL_STACK_PADDING was defined as 0 on x86_64, it went
unnoticed that the initialization of the .sp field in INIT_THREAD and some
calculations in the low level startup code do not take the padding into
account.

FRED enabled kernels require a 16 byte padding, which means that the init
task initialization and the low level startup code use the wrong stack
offset.

Subtract TOP_OF_KERNEL_STACK_PADDING in all affected places to adjust for
this.

Fixes: 65c9cc9 ("x86/fred: Reserve space for the FRED stack frame")
Fixes: 3adee77 ("x86/smpboot: Remove initial_stack on 64-bit")
Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Xin Li (Intel) <xin@zytor.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Closes: https://lore.kernel.org/oe-lkp/202402262159.183c2a37-lkp@intel.com
Link: https://lore.kernel.org/r/20240304083333.449322-1-xin@zytor.com

arch/x86/include/asm/processor.h

@@ -664,8 +664,10 @@ static __always_inline void prefetchw(const void *x)
 #else
 extern unsigned long __end_init_task[];
 
-#define INIT_THREAD {							    \
-	.sp	= (unsigned long)&__end_init_task - sizeof(struct pt_regs), \
+#define INIT_THREAD {							\
+	.sp	= (unsigned long)&__end_init_task -			\
+		  TOP_OF_KERNEL_STACK_PADDING -				\
+		  sizeof(struct pt_regs),				\
 }
 
 extern unsigned long KSTK_ESP(struct task_struct *task);

arch/x86/kernel/head_64.S

@@ -26,6 +26,7 @@
 #include <asm/apicdef.h>
 #include <asm/fixmap.h>
 #include <asm/smp.h>
+#include <asm/thread_info.h>
 
 /*
  * We are not able to switch in one step to the final KERNEL ADDRESS SPACE
@@ -66,7 +67,7 @@ SYM_CODE_START_NOALIGN(startup_64)
 	mov	%rsi, %r15
 
 	/* Set up the stack for verify_cpu() */
-	leaq	(__end_init_task - PTREGS_SIZE)(%rip), %rsp
+	leaq	(__end_init_task - TOP_OF_KERNEL_STACK_PADDING - PTREGS_SIZE)(%rip), %rsp
 
 	leaq	_text(%rip), %rdi
 

arch/x86/xen/xen-head.S

@@ -49,7 +49,7 @@ SYM_CODE_START(startup_xen)
 	ANNOTATE_NOENDBR
 	cld
 
-	leaq	(__end_init_task - PTREGS_SIZE)(%rip), %rsp
+	leaq	(__end_init_task - TOP_OF_KERNEL_STACK_PADDING - PTREGS_SIZE)(%rip), %rsp
 
 	/* Set up %gs.
 	 *