From: Dexuan Cui <decui@microsoft.com>
Date: Sat, 8 Apr 2023 14:03:39 -0700
Patch-mainline: v6.4-rc1
Subject: clocksource: hyper-v: make sure Invariant-TSC is used if it is
Git-commit: c0e96acf884a1ce91c9bdd692c6a425b83c90285
References: bsc#1206453

If Hyper-V TSC page is unavailable and Invariant-TSC is available,
currently hyperv_cs_msr (rather than Invariant-TSC) is used by default.

Use Invariant-TSC by default by downgrading hyperv_cs_msr.rating in
hv_init_tsc_clocksource(), if Invariant-TSC is available.

Signed-off-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20230408210339.15085-1-decui@microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Acked-by: Olaf Hering <ohering@suse.de>
---
 drivers/clocksource/hyperv_timer.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
--- a/drivers/clocksource/hyperv_timer.c
+++ b/drivers/clocksource/hyperv_timer.c
@@ -517,9 +517,6 @@ static bool __init hv_init_tsc_clocksource(void)
 {
 	union hv_reference_tsc_msr tsc_msr;
 
-	if (!(ms_hyperv.features & HV_MSR_REFERENCE_TSC_AVAILABLE))
-		return false;
-
 	/*
 	 * If Hyper-V offers TSC_INVARIANT, then the virtualized TSC correctly
 	 * handles frequency and offset changes due to live migration,
@@ -536,6 +533,9 @@ static bool __init hv_init_tsc_clocksource(void)
 		hyperv_cs_msr.rating = 250;
 	}
 
+	if (!(ms_hyperv.features & HV_MSR_REFERENCE_TSC_AVAILABLE))
+		return false;
+
 	hv_read_reference_counter = read_hv_clock_tsc;
 
 	/*