3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Michael Kelley <mikel...@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 <mikel...@microsoft.com>
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
Cc: "gre...@linuxfoundation.org" <gre...@linuxfoundation.org>
Cc: "de...@linuxdriverproject.org" <de...@linuxdriverproject.org>
Cc: "daniel.lezc...@linaro.org" <daniel.lezc...@linaro.org>
Cc: "virtualizat...@lists.linux-foundation.org" 
<virtualizat...@lists.linux-foundation.org>
Cc: "jgr...@suse.com" <jgr...@suse.com>
Cc: "akata...@vmware.com" <akata...@vmware.com>
Cc: "o...@aepfle.de" <o...@aepfle.de>
Cc: "a...@canonical.com" <a...@canonical.com>
Cc: vkuznets <vkuzn...@redhat.com>
Cc: "jasow...@redhat.com" <jasow...@redhat.com>
Cc: "marcelo.ce...@canonical.com" <marcelo.ce...@canonical.com>
Cc: KY Srinivasan <k...@microsoft.com>
Link: 
https://lkml.kernel.org/r/1541303219-11142-3-git-send-email-mikel...@microsoft.com
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <b...@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 = {

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