Patch "x86/apic: Fix kernel panic when booting with intremap=off and x2apic_phys" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    x86/apic: Fix kernel panic when booting with intremap=off and x2apic_phys

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-apic-fix-kernel-panic-when-booting-with-intremap.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit f09e04381df2b3bcaf607e5f250762dc709ad1dc
Author: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@xxxxxxx>
Date:   Sat Jun 17 02:52:36 2023 +0530

    x86/apic: Fix kernel panic when booting with intremap=off and x2apic_phys
    
    [ Upstream commit 85d38d5810e285d5aec7fb5283107d1da70c12a9 ]
    
    When booting with "intremap=off" and "x2apic_phys" on the kernel command
    line, the physical x2APIC driver ends up being used even when x2APIC
    mode is disabled ("intremap=off" disables x2APIC mode). This happens
    because the first compound condition check in x2apic_phys_probe() is
    false due to x2apic_mode == 0 and so the following one returns true
    after default_acpi_madt_oem_check() having already selected the physical
    x2APIC driver.
    
    This results in the following panic:
    
       kernel BUG at arch/x86/kernel/apic/io_apic.c:2409!
       invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
       CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.4.0-rc2-ver4.1rc2 #2
       Hardware name: Dell Inc. PowerEdge R6515/07PXPY, BIOS 2.3.6 07/06/2021
       RIP: 0010:setup_IO_APIC+0x9c/0xaf0
       Call Trace:
        <TASK>
        ? native_read_msr
        apic_intr_mode_init
        x86_late_time_init
        start_kernel
        x86_64_start_reservations
        x86_64_start_kernel
        secondary_startup_64_no_verify
        </TASK>
    
    which is:
    
    setup_IO_APIC:
      apic_printk(APIC_VERBOSE, "ENABLING IO-APIC IRQs\n");
      for_each_ioapic(ioapic)
            BUG_ON(mp_irqdomain_create(ioapic));
    
    Return 0 to denote that x2APIC has not been enabled when probing the
    physical x2APIC driver.
    
      [ bp: Massage commit message heavily. ]
    
    Fixes: 9ebd680bd029 ("x86, apic: Use probe routines to simplify apic selection")
    Signed-off-by: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@xxxxxxx>
    Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
    Reviewed-by: Kishon Vijay Abraham I <kvijayab@xxxxxxx>
    Reviewed-by: Vasant Hegde <vasant.hegde@xxxxxxx>
    Reviewed-by: Cyrill Gorcunov <gorcunov@xxxxxxxxx>
    Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20230616212236.1389-1-dheerajkumar.srivastava@xxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/x86/kernel/apic/x2apic_phys.c b/arch/x86/kernel/apic/x2apic_phys.c
index 6bde05a86b4ed..896bc41cb2ba7 100644
--- a/arch/x86/kernel/apic/x2apic_phys.c
+++ b/arch/x86/kernel/apic/x2apic_phys.c
@@ -97,7 +97,10 @@ static void init_x2apic_ldr(void)
 
 static int x2apic_phys_probe(void)
 {
-	if (x2apic_mode && (x2apic_phys || x2apic_fadt_phys()))
+	if (!x2apic_mode)
+		return 0;
+
+	if (x2apic_phys || x2apic_fadt_phys())
 		return 1;
 
 	return apic == &apic_x2apic_phys;