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x86/apic: Set up through-local-APIC mode on the boot CPU if 'noapic' specified

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Currently the kdump kernel becomes very slow if 'noapic' is specified.
Normal kernel doesn't have this bug.

Kernel parameter 'noapic' is used to disable IO-APIC in system for
testing or special purpose. Here the root cause is that in kdump
kernel LAPIC is disabled since commit:

  522e664644 ("x86/apic: Disable I/O APIC before shutdown of the local APIC")

In this case we need set up through-local-APIC on boot CPU in
setup_local_APIC().

In normal kernel the legacy irq mode is enabled by the BIOS. If
it is virtual wire mode, the local-APIC has been enabled and set as
through-local-APIC.

Though we fixed the regression introduced by commit 522e664644,
to further improve robustness set up the through-local-APIC mode
explicitly, do not rely on the default boot IRQ mode.

Signed-off-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: douly.fnst@cn.fujitsu.com
Cc: joro@8bytes.org
Cc: prarit@redhat.com
Cc: uobergfe@redhat.com
Link: http://lkml.kernel.org/r/20180214054656.3780-7-bhe@redhat.com
[ Rewrote the changelog. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Baoquan He 2018-02-14 13:46:56 +08:00 committed by Ingo Molnar
parent 51b146c572
commit bee3204ec3
1 changed files with 1 additions and 1 deletions
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2
arch/x86/kernel/apic/apic.c
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@ -1570,7 +1570,7 @@ static void setup_local_APIC(void)
* TODO: set up through-local-APIC from through-I/O-APIC? --macro
*/
value = apic_read(APIC_LVT0) & APIC_LVT_MASKED;
if (!cpu && (pic_mode || !value)) {
if (!cpu && (pic_mode || !value || skip_ioapic_setup)) {
value = APIC_DM_EXTINT;
apic_printk(APIC_VERBOSE, "enabled ExtINT on CPU#%d\n", cpu);
} else {