4.4-stable review patch. If anyone has any objections, please let me know.
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From: Baoquan He bhe@redhat.com
[ Upstream commit bee3204ec3c49f6f53add9c3962c9012a5c036fa ]
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 Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kernel/apic/apic.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/x86/kernel/apic/apic.c +++ b/arch/x86/kernel/apic/apic.c @@ -1368,7 +1368,7 @@ 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 {