x86/apic: Do apic driver probe for "nosmp" use case

For the "nosmp" use case, APIC initialization code uses
"APIC_SYMMETRIC_IO_NO_ROUTING" as a default interrupt mode. As per
current design, APIC drivers are not probed (via
default_setup_apic_routing()) for the above mentioned interrupt mode.
Due to missing probe, later when local APIC is initialized (for x2APIC
case), it leads to the null pointer exception due to missing allocation
of "cluster_hotplug_mask" (aka 'cmsk').

This is observed in TDX platform where x2APIC is enabled and "nosmp"
command line option is allowed.

To fix this issue, probe APIC drivers via default_setup_apic_routing()
for the APIC_SYMMETRIC_IO_NO_ROUTING interrupt mode. This will make the
code similar to APIC_SYMMETRIC_IO and APIC_VIRTUAL_WIRE interrupt modes.
Since APIC_SYMMETRIC_IO_NO_ROUTING interrupt mode is in-between
configuration between APIC_SYMMETRIC_IO and APIC_VIRTUAL_WIRE, making
the code similar to them will not have any impact (other than just
loading the apic drivers).

 BUG: kernel NULL pointer dereference, address: 0000000000000000
 #PF: supervisor write access in kernel mode
 #PF: error_code(0x0002) - not-present page
 PGD 0 P4D 0
 Oops: 0002 1 SMP NOPTI
 CPU: 0 PID: 0 Comm: swapper/0 Tainted: G Y 5.14.0-rc4-tdx-guest-v5.14-2-tdx-attest-y-vsockets+ torvalds#32
 RIP: 0010:init_x2apic_ldr+0xaf/0xc0
 Code: fb 76 65 8b 15 9a 88 fb 76 89 d2 f0 48 0f ab 50 08 5b 5d 41 5c 41 5d c3 48 8b 05 74 0d fe 02 48 c7 05 69 0d fe 02 00 00 00 00 <89> 18 eb c9 48 89 e8 eb c7 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00
 RSP: 0000:ffffffff8ae03e48 EFLAGS: 00010283
 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000200
 RDX: fffffffffffffffe RSI: 0000000000000000 RDI: 0000000000000200
 RBP: ffffffff8b7704a0 R08: 0000000000000000 R09: 0000000000000000
 R10: 0000000000000000 R11: 0000000000000007 R12: 0000000000000001
 R13: 0000000000017120 R14: ffffffff8ae13108 R15: ffffffff8aab7a20
 FS: 0000000000000000(0000) GS:ffff976a37c00000(0000) knlGS:0000000000000000
 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000000000000000 CR3: 000000017ae0c001 CR4: 00000000000606f0
 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
 DR3: 0000000000000000 DR6: 00000000fffe07f0 DR7: 0000000000000400
 Call Trace:
 setup_local_APIC+0x9b/0x350
 ? printk+0x58/0x6f
 apic_intr_mode_init+0xe5/0x109
 x86_late_time_init+0x20/0x30
 start_kernel+0x5fb/0x6b9
 secondary_startup_64_no_verify+0xbf/0xcb
 Modules linked in:
 CR2: 0000000000000000
 --[ end trace e82759a76de428f6 ]--
 RIP: 0010:init_x2apic_ldr+0xaf/0xc0

Suggested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

arch/x86/kernel/apic/apic.c

@@ -1433,6 +1433,8 @@ void __init apic_intr_mode_init(void)
 		break;
 	case APIC_SYMMETRIC_IO_NO_ROUTING:
 		pr_info("APIC: Switch to symmetric I/O mode setup in no SMP routine\n");
+		upmode = true;
+		default_setup_apic_routing();
 		break;
 	}