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    Subject[PATCH 4.9 319/329] x86/apic: Set up through-local-APIC mode on the boot CPU if noapic specified
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    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
    @@ -1403,7 +1403,7 @@ 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 {

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