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Subject[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@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@microsoft.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>
Cc: "devel@linuxdriverproject.org" <devel@linuxdriverproject.org>
Cc: "daniel.lezcano@linaro.org" <daniel.lezcano@linaro.org>
Cc: "virtualization@lists.linux-foundation.org" <virtualization@lists.linux-foundation.org>
Cc: "jgross@suse.com" <jgross@suse.com>
Cc: "akataria@vmware.com" <akataria@vmware.com>
Cc: "olaf@aepfle.de" <olaf@aepfle.de>
Cc: "apw@canonical.com" <apw@canonical.com>
Cc: vkuznets <vkuznets@redhat.com>
Cc: "jasowang@redhat.com" <jasowang@redhat.com>
Cc: "marcelo.cerri@canonical.com" <marcelo.cerri@canonical.com>
Cc: KY Srinivasan <kys@microsoft.com>
Link: https://lkml.kernel.org/r/1541303219-11142-3-git-send-email-mikelley@microsoft.com
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@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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