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From: Michael Kelley <mikelley@microsoft.com>
To: "virtualization@lists.linux-foundation.org" 
	<virtualization@lists.linux-foundation.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"daniel.lezcano@linaro.org" <daniel.lezcano@linaro.org>,
	"jgross@suse.com" <jgross@suse.com>,
	"akataria@vmware.com" <akataria@vmware.com>,
	"olaf@aepfle.de" <olaf@aepfle.de>,
	"apw@canonical.com" <apw@canonical.com>,
	vkuznets <vkuznets@redhat.com>,
	"jasowang@redhat.com" <jasowang@redhat.com>,
	"marcelo.cerri@canonical.com" <marcelo.cerri@canonical.com>,
	KY Srinivasan <kys@microsoft.com>
Cc: Michael Kelley <mikelley@microsoft.com>
Subject: [PATCH 2/2] i8253: Fix PIT shutdown quirk on Hyper-V
Date: Thu, 1 Nov 2018 17:32:32 +0000	[thread overview]
Message-ID: <1541093509-10576-1-git-send-email-mikelley@microsoft.com> (raw)

pit_shutdown() doesn't work on Hyper-V because of a quirk in the
PIT emulation. This problem exists in all versions of Hyper-V and
had not been noticed previously. When the counter register is set
to zero, the emulated PIT continues to interrupt @18.2 HZ. So
skip setting the counter register when running on Hyper-V.

Signed-off-by: Michael Kelley <mikelley@microsoft.com>
---
 drivers/clocksource/i8253.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/clocksource/i8253.c b/drivers/clocksource/i8253.c
index 9c38895..62025c8 100644
--- a/drivers/clocksource/i8253.c
+++ b/drivers/clocksource/i8253.c
@@ -10,6 +10,7 @@
 #include <linux/module.h>
 #include <linux/i8253.h>
 #include <linux/smp.h>
+#include <linux/hypervisor.h>
 
 /*
  * Protects access to I/O ports
@@ -109,8 +110,17 @@ static int pit_shutdown(struct clock_event_device *evt)
 	raw_spin_lock(&i8253_lock);
 
 	outb_p(0x30, PIT_MODE);
-	outb_p(0, PIT_CH0);
-	outb_p(0, PIT_CH0);
+
+	/*
+	 * A quirk in Hyper-V's emulation of the PIT causes the PIT
+	 * to continue to run and interrupt @18.2 Hz when the counter
+	 * register is set to zero. So skip setting the counter
+	 * register when running as a guest on Hyper-V.
+	 */
+	if (!hypervisor_is_mshyperv()) {
+		outb_p(0, PIT_CH0);
+		outb_p(0, PIT_CH0);
+	}
 
 	raw_spin_unlock(&i8253_lock);
 	return 0;
-- 
1.8.3.1


                 reply	other threads:[~2018-11-01 17:32 UTC|newest]

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