From 69b036cd78eca671fc5a0a62cfb36d990fe87194 Mon Sep 17 00:00:00 2001
From: patrick <patrick@openbsd.org>
Date: Tue, 31 Aug 2021 15:52:10 +0000
Subject: [PATCH] When running on Hyper-V, make use of its timecounter as delay
 func in case we're still using the i8254 for that.  On Hyper-V Gen 2 VMs
 there is no i8254 we can trust, so we need some kind of fallback, especially
 if there is no TSC either.

Discussed with the hackroom
ok kettenis@
---
 sys/dev/pv/hyperv.c | 12 ++++++++++++
 sys/dev/pv/pvbus.c  | 13 ++++++++++++-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/sys/dev/pv/hyperv.c b/sys/dev/pv/hyperv.c
index de753ccbfc9..dcebd3ae681 100644
--- a/sys/dev/pv/hyperv.c
+++ b/sys/dev/pv/hyperv.c
@@ -349,6 +349,18 @@ hv_gettime(struct timecounter *tc)
 	return (now);
 }
 
+void
+hv_delay(int usecs)
+{
+	uint64_t interval, start;
+
+	/* 10 MHz fixed frequency */
+	interval = (uint64_t)usecs * 10;
+	start = rdmsr(MSR_HV_TIME_REF_COUNT);
+	while (rdmsr(MSR_HV_TIME_REF_COUNT) - start < interval)
+		CPU_BUSY_CYCLE();
+}
+
 int
 hv_init_hypercall(struct hv_softc *sc)
 {
diff --git a/sys/dev/pv/pvbus.c b/sys/dev/pv/pvbus.c
index 19098a28d2f..b7bbe91ee33 100644
--- a/sys/dev/pv/pvbus.c
+++ b/sys/dev/pv/pvbus.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: pvbus.c,v 1.22 2020/08/26 03:29:06 visa Exp $	*/
+/*	$OpenBSD: pvbus.c,v 1.23 2021/08/31 15:52:10 patrick Exp $	*/
 
 /*
  * Copyright (c) 2015 Reyk Floeter <reyk@openbsd.org>
@@ -40,6 +40,9 @@
 
 #include <dev/pv/pvvar.h>
 #include <dev/pv/pvreg.h>
+#include <dev/pv/hypervreg.h>
+
+#include "hyperv.h"
 
 int has_hv_cpuid = 0;
 
@@ -297,6 +300,8 @@ pvbus_kvm(struct pvbus_hv *hv)
 	hv->hv_features = regs[0];
 }
 
+extern void hv_delay(int usecs);
+
 void
 pvbus_hyperv(struct pvbus_hv *hv)
 {
@@ -312,6 +317,12 @@ pvbus_hyperv(struct pvbus_hv *hv)
 	    HYPERV_VERSION_EBX_MAJOR_S;
 	hv->hv_minor = (regs[1] & HYPERV_VERSION_EBX_MINOR_M) >>
 	    HYPERV_VERSION_EBX_MINOR_S;
+
+#if NHYPERV > 0
+	if (hv->hv_features & CPUID_HV_MSR_TIME_REFCNT &&
+	    delay_func == i8254_delay)
+		delay_func = hv_delay;
+#endif
 }
 
 void
-- 
2.20.1