kdumpctl: use "apicid" other than "initial apicid"

We met a problem on AMD machines, when using "nr_cpus=4" for
kdump, and crash happens on cpus other than cpu0, kdump kernel
will fail to boot and eventually reset.

After some debugging, we found that it stuck at the kernel path
do_boot_cpu()-> ... ->wakeup_secondary_cpu_via_init():
 apic_icr_write(APIC_INT_LEVELTRIG|APIC_INT_ASSERT|APIC_DM_INIT,
            phys_apicid);
that is, it stuck at sending INIT from AP to BP and reset, which
is actually what "disable_cpu_apicid=X" tries to solve. Printing
the value of @phys_apicid showed that it was the value of "apicid"
other that of "initial apicid" showed by /proc/cpuinfo.

As described in x86 specification:
"In MP systems, the local APIC ID is also used as a processor ID by the
BIOS and the operating system. Some processors permit software to modify
the APIC ID. However, the ability of software to modify the APIC ID is
processor model specific. Because of this, operating system software
should avoid writing to the local APIC ID register. The value returned by
bits 31-24 of the EBX register (when the CPUID instruction is executed with a
source operand value of 1 in the EAX register) is always the Initial APIC ID
(determined by the platform initialization). This is true even if software
has changed the value in the Local APIC ID register."

From kernel commit 151e0c7de("x86, apic, kexec: Add disable_cpu_apicid
kernel parameter"), we can see in generic_processor_info(), it uses
a)read_apic_id() and b)@apicid to compare with @disabled_cpu_apicid.

a)@apicid which is actually @phys_apicid above-mentioned is from the
  following calltrace(on the problematic AMD machine):
    generic_processor_info+0x37/0x300
    acpi_register_lapic+0x30/0x90
    acpi_parse_lapic+0x40/0x50
    acpi_table_parse_entries_array+0x171/0x1de
    acpi_boot_init+0xed/0x50f
  The value of @apicid(from acpi MADT) is equal to the value of "apicid"
  showed by /proc/cpuinfo as proved by our debug printk.
b)read_apic_id() gets the value from LAPIC ID register which is "apicid"
  as well.

While the value of "initial apicid" is from cpuid instruction.

One example of "apicid" and "initial apicid" of cpu0 from /proc/cpuinfo
on AMD machine:
  apicid          : 32
  initial apicid  : 0

Therefore, we should assign /proc/cpuifo "apicid" to "disable_cpu_apicid=X".

We've never met such issue before, because we usually tested "nr_cpus=1",
and mostly on Intel machines, and "apicid" and "initial apicid" have the
same value in most cases on Intel machines.

Signed-off-by: Xunlei Pang <xlpang@redhat.com>
Acked-by: Dave Young <dyoung@redhat.com>

kdumpctl

@@ -80,15 +80,15 @@ remove_cmdline_param()
 }
 
 #
-# This function returns the "initial apicid" of the
-# boot cpu (cpu 0) if present.
+# This function returns the "apicid" of the boot
+# cpu (cpu 0) if present.
 #
-get_bootcpu_initial_apicid()
+get_bootcpu_apicid()
 {
     awk '							\
 	BEGIN { CPU = "-1"; }					\
 	$1=="processor" && $2==":"	{ CPU = $NF; }		\
-	CPU=="0" && /initial apicid/	{ print $NF; }		\
+	CPU=="0" && /^apicid/		{ print $NF; }		\
 	'							\
 	/proc/cpuinfo
 }
@@ -247,7 +247,7 @@ prepare_cmdline()
 
 	cmdline="${cmdline} ${KDUMP_COMMANDLINE_APPEND}"
 
-	id=`get_bootcpu_initial_apicid`
+	id=`get_bootcpu_apicid`
 	if [ ! -z ${id} ] ; then
 		cmdline=`append_cmdline "${cmdline}" disable_cpu_apicid ${id}`
 	fi