[PATCH 4.14 064/124] x86/hyper-v: Enable PIT shutdown quirk

Greg Kroah-Hartman gregkh at linuxfoundation.org
Mon Nov 19 16:28:38 UTC 2018

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


From: Michael Kelley <mikelley at microsoft.com>

commit 1de72c706488b7be664a601cf3843bd01e327e58 upstream.

Hyper-V emulation of the PIT has a quirk such that the normal PIT shutdown
path doesn't work, because clearing the counter register restarts the

Disable the counter clearing on PIT shutdown.

Signed-off-by: Michael Kelley <mikelley at microsoft.com>
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
Cc: "gregkh at linuxfoundation.org" <gregkh at linuxfoundation.org>
Cc: "devel at linuxdriverproject.org" <devel at linuxdriverproject.org>
Cc: "daniel.lezcano at linaro.org" <daniel.lezcano at linaro.org>
Cc: "virtualization at lists.linux-foundation.org" <virtualization at lists.linux-foundation.org>
Cc: "jgross at suse.com" <jgross at suse.com>
Cc: "akataria at vmware.com" <akataria at vmware.com>
Cc: "olaf at aepfle.de" <olaf at aepfle.de>
Cc: "apw at canonical.com" <apw at canonical.com>
Cc: vkuznets <vkuznets at redhat.com>
Cc: "jasowang at redhat.com" <jasowang at redhat.com>
Cc: "marcelo.cerri at canonical.com" <marcelo.cerri at canonical.com>
Cc: KY Srinivasan <kys at microsoft.com>
Cc: stable at vger.kernel.org
Link: https://lkml.kernel.org/r/1541303219-11142-3-git-send-email-mikelley@microsoft.com
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>

 arch/x86/kernel/cpu/mshyperv.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -20,6 +20,7 @@
 #include <linux/interrupt.h>
 #include <linux/irq.h>
 #include <linux/kexec.h>
+#include <linux/i8253.h>
 #include <asm/processor.h>
 #include <asm/hypervisor.h>
 #include <asm/hyperv.h>
@@ -243,6 +244,16 @@ static void __init ms_hyperv_init_platfo
 	if (efi_enabled(EFI_BOOT))
 		x86_platform.get_nmi_reason = hv_get_nmi_reason;
+	/*
+	 * Hyper-V VMs have a PIT emulation quirk such that zeroing the
+	 * counter register during PIT shutdown restarts the PIT. So it
+	 * continues to interrupt @18.2 HZ. Setting i8253_clear_counter
+	 * to false tells pit_shutdown() not to zero the counter so that
+	 * the PIT really is shutdown. Generation 2 VMs don't have a PIT,
+	 * and setting this value has no effect.
+	 */
+	i8253_clear_counter_on_shutdown = false;
 	 * Setup the hook to get control post apic initialization.

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