x86/cpu: Init AP exception handling from cpu_init_secondary()

SEV-ES guests require properly setup task register with which the TSS
descriptor in the GDT can be located so that the IST-type #VC exception
handler which they need to function properly, can be executed.

This setup needs to happen before attempting to load microcode in
ucode_cpu_init() on secondary CPUs which can cause such #VC exceptions.

Simplify the machinery by running that exception setup from a new function
cpu_init_secondary() and explicitly call cpu_init_exception_handling() for
the boot CPU before cpu_init(). The latter prepares for fixing and
simplifying the exception/IST setup on the boot CPU.

There should be no functional changes resulting from this patch.

[ tglx: Reworked it so cpu_init_exception_handling() stays seperate ]

Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Lai Jiangshan <laijs@linux.alibaba.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>                                                                                                                                                                                                                        
Link: https://lore.kernel.org/r/87k0o6gtvu.ffs@nanos.tec.linutronix.de

arch/x86/include/asm/processor.h

@@ -663,6 +663,7 @@ extern void load_direct_gdt(int);
 extern void load_fixmap_gdt(int);
 extern void load_percpu_segment(int);
 extern void cpu_init(void);
+extern void cpu_init_secondary(void);
 extern void cpu_init_exception_handling(void);
 extern void cr4_init(void);
 

arch/x86/kernel/cpu/common.c

@@ -1938,13 +1938,12 @@ void cpu_init_exception_handling(void)
 
 /*
  * cpu_init() initializes state that is per-CPU. Some data is already
- * initialized (naturally) in the bootstrap process, such as the GDT
+ * initialized (naturally) in the bootstrap process, such as the GDT.  We
- * and IDT. We reload them nevertheless, this function acts as a
+ * reload it nevertheless, this function acts as a 'CPU state barrier',
- * 'CPU state barrier', nothing should get across.
+ * nothing should get across.
  */
 void cpu_init(void)
 {
-	struct tss_struct *tss = this_cpu_ptr(&cpu_tss_rw);
 	struct task_struct *cur = current;
 	int cpu = raw_smp_processor_id();
 
@@ -1957,8 +1956,6 @@ void cpu_init(void)
 	    early_cpu_to_node(cpu) != NUMA_NO_NODE)
 		set_numa_node(early_cpu_to_node(cpu));
 #endif
-	setup_getcpu(cpu);
-
 	pr_debug("Initializing CPU#%d\n", cpu);
 
 	if (IS_ENABLED(CONFIG_X86_64) || cpu_feature_enabled(X86_FEATURE_VME) ||
@@ -1970,7 +1967,6 @@ void cpu_init(void)
 	 * and set up the GDT descriptor:
 	 */
 	switch_to_new_gdt(cpu);
-	load_current_idt();
 
 	if (IS_ENABLED(CONFIG_X86_64)) {
 		loadsegment(fs, 0);
@@ -1990,12 +1986,6 @@ void cpu_init(void)
 	initialize_tlbstate_and_flush();
 	enter_lazy_tlb(&init_mm, cur);
 
-	/* Initialize the TSS. */
-	tss_setup_ist(tss);
-	tss_setup_io_bitmap(tss);
-	set_tss_desc(cpu, &get_cpu_entry_area(cpu)->tss.x86_tss);
-
-	load_TR_desc();
 	/*
 	 * sp0 points to the entry trampoline stack regardless of what task
 	 * is running.
@@ -2017,6 +2007,18 @@ void cpu_init(void)
 	load_fixmap_gdt(cpu);
 }
 
+#ifdef CONFIG_SMP
+void cpu_init_secondary(void)
+{
+	/*
+	 * Relies on the BP having set-up the IDT tables, which are loaded
+	 * on this CPU in cpu_init_exception_handling().
+	 */
+	cpu_init_exception_handling();
+	cpu_init();
+}
+#endif
+
 /*
  * The microcode loader calls this upon late microcode load to recheck features,
  * only when microcode has been updated. Caller holds microcode_mutex and CPU

arch/x86/kernel/smpboot.c

@@ -232,8 +232,7 @@ static void notrace start_secondary(void *unused)
 	load_cr3(swapper_pg_dir);
 	__flush_tlb_all();
 #endif
-	cpu_init_exception_handling();
+	cpu_init_secondary();
-	cpu_init();
 	rcu_cpu_starting(raw_smp_processor_id());
 	x86_cpuinit.early_percpu_clock_init();
 	preempt_disable();

arch/x86/kernel/traps.c

@@ -1162,9 +1162,7 @@ void __init trap_init(void)
 
 	idt_setup_traps();
 
-	/*
+	cpu_init_exception_handling();
-	 * Should be a barrier for any external CPU state:
-	 */
 	cpu_init();
 
 	idt_setup_ist_traps();