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From:   Wei Liu <wei.liu@kernel.org>
To:     Linux on Hyper-V List <linux-hyperv@vger.kernel.org>
Cc:     virtualization@lists.linux-foundation.org,
        Linux Kernel List <linux-kernel@vger.kernel.org>,
        Michael Kelley <mikelley@microsoft.com>,
        Vineeth Pillai <viremana@linux.microsoft.com>,
        Sunil Muthuswamy <sunilmut@microsoft.com>,
        Nuno Das Neves <nunodasneves@linux.microsoft.com>,
        pasha.tatashin@soleen.com, Wei Liu <wei.liu@kernel.org>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        "K. Y. Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: [PATCH v6 04/16] clocksource/hyperv: use MSR-based access if running as root
Date:   Wed,  3 Feb 2021 15:04:23 +0000
Message-Id: <20210203150435.27941-5-wei.liu@kernel.org>
In-Reply-To: <20210203150435.27941-1-wei.liu@kernel.org>
References: <20210203150435.27941-1-wei.liu@kernel.org>
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When Linux runs as the root partition, the setup required for TSC page
is different. Luckily Linux also has access to the MSR based
clocksource. We can just disable the TSC page clocksource if Linux is
the root partition.

Signed-off-by: Wei Liu <wei.liu@kernel.org>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
---
 drivers/clocksource/hyperv_timer.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
index ba04cb381cd3..269a691bd2c4 100644
--- a/drivers/clocksource/hyperv_timer.c
+++ b/drivers/clocksource/hyperv_timer.c
@@ -426,6 +426,9 @@ static bool __init hv_init_tsc_clocksource(void)
 	if (!(ms_hyperv.features & HV_MSR_REFERENCE_TSC_AVAILABLE))
 		return false;
 
+	if (hv_root_partition)
+		return false;
+
 	hv_read_reference_counter = read_hv_clock_tsc;
 	phys_addr = virt_to_phys(hv_get_tsc_page());
 
-- 
2.20.1