x86/xen/smp_pv: Register fake APICs

XENPV does not use the APIC. It's just piggy packing on the infrastructure
and fiddles with global variables as it sees fit.

These global variables are going away, so let XENPV register pseudo APIC
IDs to keep the accounting correct and keep up the illusion that XEN/PV is
something sane.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Michael Kelley <mhklinux@outlook.com>
Tested-by: Sohil Mehta <sohil.mehta@intel.com>
Link: https://lore.kernel.org/r/20240213210251.940043512@linutronix.de

arch/x86/xen/smp_pv.c

@@ -29,6 +29,7 @@
 #include <asm/idtentry.h>
 #include <asm/desc.h>
 #include <asm/cpu.h>
+#include <asm/apic.h>
 #include <asm/io_apic.h>
 
 #include <xen/interface/xen.h>
@@ -150,34 +151,16 @@ int xen_smp_intr_init_pv(unsigned int cpu)
 
 static void __init xen_pv_smp_config(void)
 {
-	int i, rc;
-	unsigned int subtract = 0;
-
-	num_processors = 0;
-	disabled_cpus = 0;
-	for (i = 0; i < nr_cpu_ids; i++) {
-		rc = HYPERVISOR_vcpu_op(VCPUOP_is_up, i, NULL);
-		if (rc >= 0) {
-			num_processors++;
-			set_cpu_possible(i, true);
-		} else {
-			set_cpu_possible(i, false);
-			set_cpu_present(i, false);
-			subtract++;
-		}
+	u32 apicid = 0;
+	int i;
+
+	topology_register_boot_apic(apicid++);
+
+	for (i = 1; i < nr_cpu_ids; i++) {
+		if (HYPERVISOR_vcpu_op(VCPUOP_is_up, i, NULL) < 0)
+			break;
+		topology_register_apic(apicid++, CPU_ACPIID_INVALID, true);
 	}
-#ifdef CONFIG_HOTPLUG_CPU
-	/* This is akin to using 'nr_cpus' on the Linux command line.
-	 * Which is OK as when we use 'dom0_max_vcpus=X' we can only
-	 * have up to X, while nr_cpu_ids is greater than X. This
-	 * normally is not a problem, except when CPU hotplugging
-	 * is involved and then there might be more than X CPUs
-	 * in the guest - which will not work as there is no
-	 * hypercall to expand the max number of VCPUs an already
-	 * running guest has. So cap it up to X. */
-	if (subtract)
-		set_nr_cpu_ids(nr_cpu_ids - subtract);
-#endif
 	/* Pretend to be a proper enumerated system */
 	smp_found_config = 1;
 }