[PATCH] x86: x86_32 kdump boot on cpu != 0

[Ed Swierk]

Booting an x86_32 SMP kernel via kdump fails if the boot CPU has local
APIC ID != 0, with a panic:

  Boot APIC ID in local APIC unexpected (1 vs 0)

MP_processor_info() sets boot_cpu_physical_apicid to 0 based on the
mptable.  But this variable needs to be set to 1 later on to reflect the
actual local APIC ID.  (Setting it to 1 right off the bat causes
generic_processor_info() to complain about an "apic version mismatch",
which I don't understand.)

This change restores the apic_64.c logic, which existed prior to the
merge with apic_32.c, and allows the kdump kernel to boot.
 
Signed-off-by: Ed Swierk <eswierk@xxxxxxxxxxxxxxxxxx>
---
 arch/x86/kernel/apic/apic.c |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index f287092..b45c764 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1563,8 +1563,7 @@ void __init init_apic_mappings(void)
 	 * Fetch the APIC ID of the BSP in case we have a
 	 * default configuration (or the MP table is broken).
 	 */
-	if (boot_cpu_physical_apicid == -1U)
-		boot_cpu_physical_apicid = read_apic_id();
+	boot_cpu_physical_apicid = read_apic_id();
 }
 
 /*


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