x86/smpboot: Restrict soft_restart_cpu() to SEV

Now that the CPU0 hotplug cruft is gone, the only user is AMD SEV.

Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Tested-by: Michael Kelley <[email protected]>
Tested-by: Oleksandr Natalenko <[email protected]>
Tested-by: Helge Deller <[email protected]> # parisc
Tested-by: Guilherme G. Piccoli <[email protected]> # Steam Deck
Link: https://lore.kernel.org/r/[email protected]

Author: KAGA-KOKO

arch/x86/kernel/callthunks.c

@@ -133,7 +133,7 @@ static bool skip_addr(void *dest)
 	/* Accounts directly */
 	if (dest == ret_from_fork)
 		return true;
-#ifdef CONFIG_HOTPLUG_CPU
+#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_AMD_MEM_ENCRYPT)
 	if (dest == soft_restart_cpu)
 		return true;
 #endif

arch/x86/kernel/head_32.S

@@ -138,20 +138,6 @@ SYM_CODE_START(startup_32)
 	jmp .Ldefault_entry
 SYM_CODE_END(startup_32)
 
-#ifdef CONFIG_HOTPLUG_CPU
-/*
- * Entry point for soft restart of a CPU. Invoked from xxx_play_dead() for
- * restarting the boot CPU or for restarting SEV guest CPUs after CPU hot
- * unplug. Everything is set up already except the stack.
- */
-SYM_FUNC_START(soft_restart_cpu)
-	movl initial_stack, %ecx
-	movl %ecx, %esp
-	call *(initial_code)
-1:	jmp 1b
-SYM_FUNC_END(soft_restart_cpu)
-#endif
-
 /*
  * Non-boot CPU entry point; entered from trampoline.S
  * We can't lgdt here, because lgdt itself uses a data segment, but

arch/x86/kernel/head_64.S

@@ -375,7 +375,7 @@ SYM_CODE_END(secondary_startup_64)
 #include "verify_cpu.S"
 #include "sev_verify_cbit.S"
 
-#ifdef CONFIG_HOTPLUG_CPU
+#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_AMD_MEM_ENCRYPT)
 /*
  * Entry point for soft restart of a CPU. Invoked from xxx_play_dead() for
  * restarting the boot CPU or for restarting SEV guest CPUs after CPU hot