linux-kernel - [PATCH v3] x86/apic: Do apic driver probe for "nosmp" use case

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Date:   Sat, 16 Apr 2022 02:45:32 +0000
From:   Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>
Cc:     linux-kernel@...r.kernel.org,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Tony Luck <tony.luck@...el.com>
Subject: [PATCH v3] 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, MADT/MP table
exist 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).

Since default_setup_apic_routing() is called for all cases with a break
statement, move it outside the switch-case.

 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
 RIP: 0010:init_x2apic_ldr+0xaf/0xc0
 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@...ux.intel.com>
Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Reviewed-by: Tony Luck <tony.luck@...el.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
---

Changes since v1:
 * Removed upmode = true change for APIC_SYMMETRIC_IO_NO_ROUTING case.
 * Made some minor changes to commit log (like removing register dump
   in panic log)

 arch/x86/kernel/apic/apic.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index b70344bf6600..f4d12db8add0 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1419,22 +1419,21 @@ void __init apic_intr_mode_init(void)
 		return;
 	case APIC_VIRTUAL_WIRE:
 		pr_info("APIC: Switch to virtual wire mode setup\n");
-		default_setup_apic_routing();
 		break;
 	case APIC_VIRTUAL_WIRE_NO_CONFIG:
 		pr_info("APIC: Switch to virtual wire mode setup with no configuration\n");
 		upmode = true;
-		default_setup_apic_routing();
 		break;
 	case APIC_SYMMETRIC_IO:
 		pr_info("APIC: Switch to symmetric I/O mode setup\n");
-		default_setup_apic_routing();
 		break;
 	case APIC_SYMMETRIC_IO_NO_ROUTING:
 		pr_info("APIC: Switch to symmetric I/O mode setup in no SMP routine\n");
 		break;
 	}

+	default_setup_apic_routing();
+
 	if (x86_platform.apic_post_init)
 		x86_platform.apic_post_init();

-- 
2.25.1