x86/smp: Split sending INIT IPI out into a helper function

Putting CPUs into INIT is a safer place during kexec() to park CPUs.

Split the INIT assert/deassert sequence out so it can be reused.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ashok Raj <ashok.raj@intel.com>
Link: https://lore.kernel.org/r/20230615193330.551157083@linutronix.de

Author: KAGA-KOKO

arch/x86/kernel/smpboot.c

@@ -853,47 +853,38 @@ wakeup_secondary_cpu_via_nmi(int apicid, unsigned long start_eip)
 	return (send_status | accept_status);
 }
 
-static int
-wakeup_secondary_cpu_via_init(int phys_apicid, unsigned long start_eip)
+static void send_init_sequence(int phys_apicid)
 {
-	unsigned long send_status = 0, accept_status = 0;
-	int maxlvt, num_starts, j;
+	int maxlvt = lapic_get_maxlvt();
 
-	maxlvt = lapic_get_maxlvt();
-
-	/*
-	 * Be paranoid about clearing APIC errors.
-	 */
+	/* Be paranoid about clearing APIC errors. */
 	if (APIC_INTEGRATED(boot_cpu_apic_version)) {
-		if (maxlvt > 3)		/* Due to the Pentium erratum 3AP.  */
+		/* Due to the Pentium erratum 3AP.  */
+		if (maxlvt > 3)
 			apic_write(APIC_ESR, 0);
 		apic_read(APIC_ESR);
 	}
 
-	pr_debug("Asserting INIT\n");
-
-	/*
-	 * Turn INIT on target chip
-	 */
-	/*
-	 * Send IPI
-	 */
-	apic_icr_write(APIC_INT_LEVELTRIG | APIC_INT_ASSERT | APIC_DM_INIT,
-		       phys_apicid);
-
-	pr_debug("Waiting for send to finish...\n");
-	send_status = safe_apic_wait_icr_idle();
+	/* Assert INIT on the target CPU */
+	apic_icr_write(APIC_INT_LEVELTRIG | APIC_INT_ASSERT | APIC_DM_INIT, phys_apicid);
+	safe_apic_wait_icr_idle();
 
 	udelay(init_udelay);
 
-	pr_debug("Deasserting INIT\n");
-
-	/* Target chip */
-	/* Send IPI */
+	/* Deassert INIT on the target CPU */
 	apic_icr_write(APIC_INT_LEVELTRIG | APIC_DM_INIT, phys_apicid);
+	safe_apic_wait_icr_idle();
+}
 
-	pr_debug("Waiting for send to finish...\n");
-	send_status = safe_apic_wait_icr_idle();
+/*
+ * Wake up AP by INIT, INIT, STARTUP sequence.
+ */
+static int wakeup_secondary_cpu_via_init(int phys_apicid, unsigned long start_eip)
+{
+	unsigned long send_status = 0, accept_status = 0;
+	int num_starts, j, maxlvt = lapic_get_maxlvt();
+
+	send_init_sequence(phys_apicid);
 
 	mb();