* [PATCH 2/2] i8253: Fix PIT shutdown quirk on Hyper-V
@ 2018-11-01 17:32 Michael Kelley
0 siblings, 0 replies; only message in thread
From: Michael Kelley @ 2018-11-01 17:32 UTC (permalink / raw)
To: virtualization, linux-kernel, tglx, daniel.lezcano, jgross,
akataria, olaf, apw, vkuznets, jasowang, marcelo.cerri,
KY Srinivasan
Cc: Michael Kelley
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
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2018-11-01 17:32 [PATCH 2/2] i8253: Fix PIT shutdown quirk on Hyper-V Michael Kelley
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