Linux Virtualization - Jan 2021 - [PATCH v5 05/16] clocksource/hyperv: use MSR-based access if running as root

On Wed, Jan 20, 2021 at 7:01 AM Wei Liu <wei.liu at kernel.org>
wrote:
>
> When Linux runs as the root partition, the setup required for TSC page
> is different.
Why would we need a TSC page as a clock source for root partition at
all? I think the above can be removed.

 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 at kernel.org>
> Acked-by: Daniel Lezcano <daniel.lezcano at linaro.org>
> ---
>  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;
> +
Reviewed-by: Pavel Tatashin <pasha.tatashin at soleen.com>