linux-kernel - [PATCH 4.4 256/268] x86/apic: Set up through-local-APIC mode on the boot CPU if noapic specified

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Message-Id: <20180528100232.051254717@linuxfoundation.org>
Date:   Mon, 28 May 2018 12:03:50 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Baoquan He <bhe@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        douly.fnst@...fujitsu.com, joro@...tes.org, prarit@...hat.com,
        uobergfe@...hat.com, Ingo Molnar <mingo@...nel.org>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 4.4 256/268] x86/apic: Set up through-local-APIC mode on the boot CPU if noapic specified

4.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Baoquan He <bhe@...hat.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@...hat.com>
Reviewed-by: Eric W. Biederman <ebiederm@...ssion.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: douly.fnst@...fujitsu.com
Cc: joro@...tes.org
Cc: prarit@...hat.com
Cc: uobergfe@...hat.com
Link: http://lkml.kernel.org/r/20180214054656.3780-7-bhe@redhat.com
[ Rewrote the changelog. ]
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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 {