4.4-stable review patch. If anyone has any objections, please let me know.
------------------ From: Baoquan He <b...@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 <b...@redhat.com> Reviewed-by: Eric W. Biederman <ebied...@xmission.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Thomas Gleixner <t...@linutronix.de> Cc: douly.f...@cn.fujitsu.com Cc: j...@8bytes.org Cc: pra...@redhat.com Cc: uober...@redhat.com Link: http://lkml.kernel.org/r/20180214054656.3780-7-...@redhat.com [ Rewrote the changelog. ] Signed-off-by: Ingo Molnar <mi...@kernel.org> Signed-off-by: Sasha Levin <alexander.le...@microsoft.com> Signed-off-by: Greg Kroah-Hartman <gre...@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 {