clocksource/hyperv: use MSR-based access if running as root

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>
Link: https://lore.kernel.org/r/20210203150435.27941-5-wei.liu@kernel.org

diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
index ba04cb381cd3fd6133dc54bc7749f7b05c52273d..269a691bd2c4502485261a59baa7a73a718692bb 100644 (file)
--- 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());