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

From: Wei Liu <wei.liu at kernel.org> Sent: Wednesday, January 20, 2021
4:01 AM
> 
> 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 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;
> +
>  	hv_read_reference_counter = read_hv_clock_tsc;
>  	phys_addr = virt_to_phys(hv_get_tsc_page());
> 
> --
> 2.20.1
Reviewed-by: Michael Kelley <mikelley at microsoft.com>