linux-kernel - Re: [PATCH v3] x86/tsc: Disable clocksource watchdog for TSC on recent UV

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Message-ID: <aMLMzPwwjmr19fRU@hpe.com>
Date: Thu, 11 Sep 2025 08:21:16 -0500
From: Dimitri Sivanich <sivanich@....com>
To: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc: Jiri Wiesner <jwiesner@...e.de>, Thomas Gleixner <tglx@...utronix.de>,
        Jonathan Corbet <corbet@....net>, Steve Wahl <steve.wahl@....com>,
        Justin Ernst <justin.ernst@....com>, Kyle Meyer <kyle.meyer@....com>,
        Russ Anderson <russ.anderson@....com>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v3] x86/tsc: Disable clocksource watchdog for TSC on
 recent UV

On Wed, Aug 20, 2025 at 02:54:16PM -0500, Dimitri Sivanich wrote:
> Disable clocksource watchdog checking on recent and future UV platforms
> to avoid false positives.
> 
> Commits 'b50db7095fe0 ("x86/tsc: Disable clocksource watchdog for TSC on
> qualified platforms")' and '233756a640be ("Extend watchdog check exemption
> to 4-Sockets platform")' were introduced to avoid an issue where the TSC
> is falsely declared unstable by exempting qualified platforms of up to
> 4-sockets from TSC clocksource watchdog checking.  Extend that exemption
> to include recent and future UV platforms.
> 
> Signed-off-by: Dimitri Sivanich <sivanich@....com>
> ---
> 
> Version 3:  Fixes a build error in the X86 32-bit build.
> 
> Version 2:  Fixes a build error that occurs when UV is not configured.
> 
>  arch/x86/include/asm/uv/uv.h     | 3 +++
>  arch/x86/include/asm/uv/uv_hub.h | 2 ++
>  arch/x86/kernel/tsc.c            | 3 ++-
>  3 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/uv/uv.h b/arch/x86/include/asm/uv/uv.h
> index 648eb23fe7f0..f1aebdf85e68 100644
> --- a/arch/x86/include/asm/uv/uv.h
> +++ b/arch/x86/include/asm/uv/uv.h
> @@ -38,6 +38,9 @@ static inline int is_uv_system(void)	{ return 0; }
>  static inline int is_uv_hubbed(int uv)	{ return 0; }
>  static inline void uv_cpu_init(void)	{ }
>  static inline void uv_system_init(void)	{ }
> +static inline int is_uvx_hub(void) { return 0; }
> +static inline int is_uvy_hub(void) { return 0; }
> +static inline int is_uv_hub(void) { return 0; }
>  
>  #endif	/* X86_UV */
>  
> diff --git a/arch/x86/include/asm/uv/uv_hub.h b/arch/x86/include/asm/uv/uv_hub.h
> index ea877fd83114..6e085ce8fc02 100644
> --- a/arch/x86/include/asm/uv/uv_hub.h
> +++ b/arch/x86/include/asm/uv/uv_hub.h
> @@ -246,6 +246,7 @@ static inline int is_uv5_hub(void) { return is_uv(UV5); }
>   * then test if is UV4.
>   */
>  
> +#ifdef CONFIG_X86_UV
>  /* UVX class: UV2,3,4 */
>  static inline int is_uvx_hub(void) { return is_uv(UVX); }
>  
> @@ -254,6 +255,7 @@ static inline int is_uvy_hub(void) { return is_uv(UVY); }
>  
>  /* Any UV Hubbed System */
>  static inline int is_uv_hub(void) { return is_uv(UV_ANY); }
> +#endif
>  
>  union uvh_apicid {
>      unsigned long       v;
> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> index 87e749106dda..a9f97d423ab0 100644
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -32,6 +32,7 @@
>  #include <asm/msr.h>
>  #include <asm/topology.h>
>  #include <asm/uv/uv.h>
> +#include <asm/uv/uv_hub.h>
>  #include <asm/sev.h>
>  
>  unsigned int __read_mostly cpu_khz;	/* TSC clocks / usec, not used here */
> @@ -1261,7 +1262,7 @@ static void __init check_system_tsc_reliable(void)
>  	if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) &&
>  	    boot_cpu_has(X86_FEATURE_NONSTOP_TSC) &&
>  	    boot_cpu_has(X86_FEATURE_TSC_ADJUST) &&
> -	    topology_max_packages() <= 4)
> +	    (topology_max_packages() <= 4 || is_uvy_hub()))
>  		tsc_disable_clocksource_watchdog();
>  }
>  
> -- 
> 2.43.0

Just a friendly reminder about this patch.