linux-kernel - RE: [PATCH AUTOSEL 6.0 13/44] clocksource/drivers/hyperv: add data structure for reference TSC MSR

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Message-ID: <SN6PR2101MB1693A83DF44A95B439532F9DD7089@SN6PR2101MB1693.namprd21.prod.outlook.com>
Date:   Sat, 19 Nov 2022 05:37:16 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Sasha Levin <sashal@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Anirudh Rayabharam <anrayabh@...ux.microsoft.com>,
        Wei Liu <wei.liu@...nel.org>
CC:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Dexuan Cui <decui@...rosoft.com>,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: RE: [PATCH AUTOSEL 6.0 13/44] clocksource/drivers/hyperv: add data
 structure for reference TSC MSR

From: Sasha Levin <sashal@...nel.org> Sent: Friday, November 18, 2022 6:11 PM
> 
> From: Anirudh Rayabharam <anrayabh@...ux.microsoft.com>
> 
> [ Upstream commit 4ad1aa571214e8d6468a1806794d987b374b5a08 ]
> 
> Add a data structure to represent the reference TSC MSR similar to
> other MSRs. This simplifies the code for updating the MSR.
> 
> Signed-off-by: Anirudh Rayabharam <anrayabh@...ux.microsoft.com>
> Reviewed-by: Michael Kelley <mikelley@...rosoft.com>
> Link: https://lore.kernel.org/all/20221027095729.1676394-2-anrayabh@linux.microsoft.com/
> Signed-off-by: Wei Liu <wei.liu@...nel.org>
> Signed-off-by: Sasha Levin <sashal@...nel.org>

Sasha -- I don't think this patch needs to be backported to any stable versions.  Anirudh
or Wei Liu, can you confirm?  The patch is more about enabling a new scenario than fixing a bug.

Michael

> ---
>  drivers/clocksource/hyperv_timer.c | 29 +++++++++++++++--------------
>  include/asm-generic/hyperv-tlfs.h  |  9 +++++++++
>  2 files changed, 24 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
> index bb47610bbd1c..18de1f439ffd 100644
> --- a/drivers/clocksource/hyperv_timer.c
> +++ b/drivers/clocksource/hyperv_timer.c
> @@ -21,6 +21,7 @@
>  #include <linux/interrupt.h>
>  #include <linux/irq.h>
>  #include <linux/acpi.h>
> +#include <linux/hyperv.h>
>  #include <clocksource/hyperv_timer.h>
>  #include <asm/hyperv-tlfs.h>
>  #include <asm/mshyperv.h>
> @@ -395,25 +396,25 @@ static u64 notrace read_hv_sched_clock_tsc(void)
> 
>  static void suspend_hv_clock_tsc(struct clocksource *arg)
>  {
> -	u64 tsc_msr;
> +	union hv_reference_tsc_msr tsc_msr;
> 
>  	/* Disable the TSC page */
> -	tsc_msr = hv_get_register(HV_REGISTER_REFERENCE_TSC);
> -	tsc_msr &= ~BIT_ULL(0);
> -	hv_set_register(HV_REGISTER_REFERENCE_TSC, tsc_msr);
> +	tsc_msr.as_uint64 = hv_get_register(HV_REGISTER_REFERENCE_TSC);
> +	tsc_msr.enable = 0;
> +	hv_set_register(HV_REGISTER_REFERENCE_TSC, tsc_msr.as_uint64);
>  }
> 
> 
>  static void resume_hv_clock_tsc(struct clocksource *arg)
>  {
>  	phys_addr_t phys_addr = virt_to_phys(&tsc_pg);
> -	u64 tsc_msr;
> +	union hv_reference_tsc_msr tsc_msr;
> 
>  	/* Re-enable the TSC page */
> -	tsc_msr = hv_get_register(HV_REGISTER_REFERENCE_TSC);
> -	tsc_msr &= GENMASK_ULL(11, 0);
> -	tsc_msr |= BIT_ULL(0) | (u64)phys_addr;
> -	hv_set_register(HV_REGISTER_REFERENCE_TSC, tsc_msr);
> +	tsc_msr.as_uint64 = hv_get_register(HV_REGISTER_REFERENCE_TSC);
> +	tsc_msr.enable = 1;
> +	tsc_msr.pfn = HVPFN_DOWN(phys_addr);
> +	hv_set_register(HV_REGISTER_REFERENCE_TSC, tsc_msr.as_uint64);
>  }
> 
>  #ifdef HAVE_VDSO_CLOCKMODE_HVCLOCK
> @@ -495,7 +496,7 @@ static __always_inline void hv_setup_sched_clock(void
> *sched_clock) {}
> 
>  static bool __init hv_init_tsc_clocksource(void)
>  {
> -	u64		tsc_msr;
> +	union hv_reference_tsc_msr tsc_msr;
>  	phys_addr_t	phys_addr;
> 
>  	if (!(ms_hyperv.features & HV_MSR_REFERENCE_TSC_AVAILABLE))
> @@ -530,10 +531,10 @@ static bool __init hv_init_tsc_clocksource(void)
>  	 * (which already has at least the low 12 bits set to zero since
>  	 * it is page aligned). Also set the "enable" bit, which is bit 0.
>  	 */
> -	tsc_msr = hv_get_register(HV_REGISTER_REFERENCE_TSC);
> -	tsc_msr &= GENMASK_ULL(11, 0);
> -	tsc_msr = tsc_msr | 0x1 | (u64)phys_addr;
> -	hv_set_register(HV_REGISTER_REFERENCE_TSC, tsc_msr);
> +	tsc_msr.as_uint64 = hv_get_register(HV_REGISTER_REFERENCE_TSC);
> +	tsc_msr.enable = 1;
> +	tsc_msr.pfn = HVPFN_DOWN(phys_addr);
> +	hv_set_register(HV_REGISTER_REFERENCE_TSC, tsc_msr.as_uint64);
> 
>  	clocksource_register_hz(&hyperv_cs_tsc, NSEC_PER_SEC/100);
> 
> diff --git a/include/asm-generic/hyperv-tlfs.h b/include/asm-generic/hyperv-tlfs.h
> index fdce7a4cfc6f..b17c6eeb9afa 100644
> --- a/include/asm-generic/hyperv-tlfs.h
> +++ b/include/asm-generic/hyperv-tlfs.h
> @@ -102,6 +102,15 @@ struct ms_hyperv_tsc_page {
>  	volatile s64 tsc_offset;
>  } __packed;
> 
> +union hv_reference_tsc_msr {
> +	u64 as_uint64;
> +	struct {
> +		u64 enable:1;
> +		u64 reserved:11;
> +		u64 pfn:52;
> +	} __packed;
> +};
> +
>  /*
>   * The guest OS needs to register the guest ID with the hypervisor.
>   * The guest ID is a 64 bit entity and the structure of this ID is
> --
> 2.35.1