linux-kernel - RE: [PATCH v5 05/16] clocksource/hyperv: use MSR-based access if running as root

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Message-ID: <MWHPR21MB159358DEBC6EA386763B788FD7BC9@MWHPR21MB1593.namprd21.prod.outlook.com>
Date:   Tue, 26 Jan 2021 00:34:26 +0000
From:   Michael Kelley <mikelley@...rosoft.com>
To:     Wei Liu <wei.liu@...nel.org>,
        Linux on Hyper-V List <linux-hyperv@...r.kernel.org>
CC:     "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        Linux Kernel List <linux-kernel@...r.kernel.org>,
        Vineeth Pillai <viremana@...ux.microsoft.com>,
        Sunil Muthuswamy <sunilmut@...rosoft.com>,
        Nuno Das Neves <nunodasneves@...ux.microsoft.com>,
        "pasha.tatashin@...een.com" <pasha.tatashin@...een.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: RE: [PATCH v5 05/16] clocksource/hyperv: use MSR-based access if
 running as root

From: Wei Liu <wei.liu@...nel.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@...nel.org>
> Acked-by: Daniel Lezcano <daniel.lezcano@...aro.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@...rosoft.com>