Linux Virtualization - Feb 2019 - [PATCH 3.16 140/305] x86/hyper-v: Enable PIT shutdown quirk

3.16.63-rc1 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
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>
Link: https://lkml.kernel.org/r/1541303219-11142-3-git-send-email-mikelley at
microsoft.com
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben at decadent.org.uk>
---
 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
@@ -18,6 +18,7 @@
 #include <linux/efi.h>
 #include <linux/interrupt.h>
 #include <linux/irq.h>
+#include <linux/i8253.h>
 #include <asm/processor.h>
 #include <asm/hypervisor.h>
 #include <asm/hyperv.h>
@@ -143,6 +144,16 @@ static void __init ms_hyperv_init_platfo
 	no_timer_check = 1;
 #endif
 
+	/*
+	 * 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;
+
 }
 
 const __refconst struct hypervisor_x86 x86_hyper_ms_hyperv = {