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Message-ID: <1539795298-11804-1-git-send-email-mikelley@microsoft.com>
Date: Wed, 17 Oct 2018 16:55:16 +0000
From: Michael Kelley <mikelley@...rosoft.com>
To: "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"x86@...nel.org" <x86@...nel.org>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
"olaf@...fle.de" <olaf@...fle.de>,
"apw@...onical.com" <apw@...onical.com>,
vkuznets <vkuznets@...hat.com>,
"jasowang@...hat.com" <jasowang@...hat.com>,
"marcelo.cerri@...onical.com" <marcelo.cerri@...onical.com>,
Stephen Hemminger <sthemmin@...rosoft.com>,
KY Srinivasan <kys@...rosoft.com>
CC: Michael Kelley <mikelley@...rosoft.com>
Subject: [PATCH char-misc 1/1] x86/hyperv: Fix PIT shutdown quirk
pit_shutdown() doesn't work on Hyper-V because of a quirk in the
PIT emulation. After shutdown the emulated PIT continues to interrupt
every 18.2 seconds. This problem exists in all versions of Hyper-V
and just had not previously been noticed. So replace the normal PIT
shutdown function with an alternate version that works on Hyper-V.
The alternate shutdown function could go in the i8253.c module,
but it seems better to keep the hack with the Hyper-V code rather
than clutter up i8253.c with #ifdef CONFIG_HYPERV.
Signed-off-by: Michael Kelley <mikelley@...rosoft.com>
---
arch/x86/hyperv/hv_init.c | 31 +++++++++++++++++++++++++++++++
1 file changed, 31 insertions(+)
diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 7abb09e..54326af 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -32,6 +32,9 @@
#include <linux/slab.h>
#include <linux/cpuhotplug.h>
+#include <linux/io.h>
+#include <linux/i8253.h>
+
#ifdef CONFIG_HYPERV_TSCPAGE
static struct ms_hyperv_tsc_page *tsc_pg;
@@ -97,6 +100,26 @@ static u64 read_hv_clock_msr(struct clocksource *arg)
u32 hv_max_vp_index;
+#if defined(CONFIG_CLKEVT_I8253)
+/*
+ * Hyper-V emulation of the PIT has a quirk such that the
+ * normal i8253 pit_shutdown() routine doesn't stop the PIT.
+ * It keeps interrupting every 18.2 seconds. This alternate
+ * shutdown routine mirrors the normal one, but does not
+ * set the counter value to zero.
+ */
+static int hyperv_pit_shutdown(struct clock_event_device *evt)
+{
+ if (!clockevent_state_oneshot(evt) && !clockevent_state_periodic(evt))
+ return 0;
+
+ raw_spin_lock(&i8253_lock);
+ outb_p(0x30, PIT_MODE);
+ raw_spin_unlock(&i8253_lock);
+ return 0;
+}
+#endif
+
static int hv_cpu_init(unsigned int cpu)
{
u64 msr_vp_index;
@@ -325,6 +348,14 @@ void __init hyperv_init(void)
if (cpuhp < 0)
goto free_vp_assist_page;
+#if defined(CONFIG_CLKEVT_I8253)
+ /*
+ * Override the PIT shutdown routine due to a quirk in
+ * Hyper-V emulation of the PIT.
+ */
+ i8253_clockevent.set_state_shutdown = hyperv_pit_shutdown;
+#endif
+
/*
* Setup the hypercall page and enable hypercalls.
* 1. Register the guest ID
--
1.8.3.1
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