linux-kernel - RE: [PATCH 2/7] clocksource/drivers: Suspend/resume Hyper-V clocksource for hibernation

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Message-ID: <MWHPR21MB0784EBA3631A184D23CF6260D7DC0@MWHPR21MB0784.namprd21.prod.outlook.com>
Date:   Tue, 30 Jul 2019 22:23:23 +0000
From:   Michael Kelley <mikelley@...rosoft.com>
To:     Dexuan Cui <decui@...rosoft.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Sasha Levin <Alexander.Levin@...rosoft.com>,
        "sashal@...nel.org" <sashal@...nel.org>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 2/7] clocksource/drivers: Suspend/resume Hyper-V
 clocksource for hibernation

From: Dexuan Cui <decui@...rosoft.com> Sent: Monday, July 8, 2019 10:29 PM
> 
> This is needed for hibernation, e.g. when we resume the old kernel, we need
> to disable the "current" kernel's TSC page and then resume the old kernel's.
> 
> Signed-off-by: Dexuan Cui <decui@...rosoft.com>
> ---
>  drivers/clocksource/hyperv_timer.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
> index ba2c79e6..41c31a7 100644
> --- a/drivers/clocksource/hyperv_timer.c
> +++ b/drivers/clocksource/hyperv_timer.c
> @@ -237,12 +237,37 @@ static u64 read_hv_clock_tsc(struct clocksource *arg)
>  	return read_hv_sched_clock_tsc();
>  }
> 
> +static void suspend_hv_clock_tsc(struct clocksource *arg)
> +{
> +	u64 tsc_msr;
> +
> +	/* Disable the TSC page */
> +	hv_get_reference_tsc(tsc_msr);
> +	tsc_msr &= ~BIT_ULL(0);
> +	hv_set_reference_tsc(tsc_msr);
> +}
> +
> +
> +static void resume_hv_clock_tsc(struct clocksource *arg)
> +{
> +	phys_addr_t phys_addr = page_to_phys(vmalloc_to_page(tsc_pg));
> +	u64 tsc_msr;
> +
> +	/* Re-enable the TSC page */
> +	hv_get_reference_tsc(tsc_msr);
> +	tsc_msr &= GENMASK_ULL(11, 0);
> +	tsc_msr |= BIT_ULL(0) | (u64)phys_addr;
> +	hv_set_reference_tsc(tsc_msr);
> +}
> +
>  static struct clocksource hyperv_cs_tsc = {
>  	.name	= "hyperv_clocksource_tsc_page",
>  	.rating	= 400,
>  	.read	= read_hv_clock_tsc,
>  	.mask	= CLOCKSOURCE_MASK(64),
>  	.flags	= CLOCK_SOURCE_IS_CONTINUOUS,
> +	.suspend= suspend_hv_clock_tsc,
> +	.resume	= resume_hv_clock_tsc,
>  };
>  #endif
> 
> --
> 1.8.3.1

Reviewed-by: Michael Kelley <mikelley@...rosoft.com>