Linux Virtualization - Nov 2018 - Patch "x86/hyper-v: Enable PIT shutdown quirk" has been added to the 4.18-stable tree

This is a note to let you know that I've just added the patch titled

    x86/hyper-v: Enable PIT shutdown quirk

to the 4.18-stable tree which can be found at:
   
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-hyper-v-enable-pit-shutdown-quirk.patch
and it can be found in the queue-4.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable at vger.kernel.org> know about it.

>From 1de72c706488b7be664a601cf3843bd01e327e58 Mon Sep 17 00:00:00 2001
From: Michael Kelley <mikelley at microsoft.com>
Date: Sun, 4 Nov 2018 03:48:57 +0000
Subject: x86/hyper-v: Enable PIT shutdown quirk

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
timer.

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 at
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-tlfs.h>
@@ -285,6 +286,16 @@ 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;
+
 #if IS_ENABLED(CONFIG_HYPERV)
 	/*
 	 * Setup the hook to get control post apic initialization.


Patches currently in stable-queue which might be from mikelley at microsoft.com
are

queue-4.18/x86-hyper-v-enable-pit-shutdown-quirk.patch
queue-4.18/clockevents-drivers-i8253-add-support-for-pit-shutdown-quirk.patch