linux-kernel - Re: [PATCH] Handle Ice Lake MONITOR erratum

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Message-ID: <aAc7Y5x_frQUB2Gc@gmail.com>
Date: Tue, 22 Apr 2025 08:46:59 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, andrew.cooper3@...rix.com,
	Len Brown <len.brown@...el.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	stable@...r.kernel.org
Subject: Re: [PATCH] Handle Ice Lake MONITOR erratum


* Dave Hansen <dave.hansen@...ux.intel.com> wrote:

> 
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> Andrew Cooper reported some boot issues on Ice Lake servers when
> running Xen that he tracked down to MWAIT not waking up. Do the safe
> thing and consider them buggy since there's a published erratum.
> Note: I've seen no reports of this occurring on Linux.
> 
> Add Ice Lake servers to the list of shaky MONITOR implementations with
> no workaround available. Also, before the if() gets too unwieldy, move
> it over to a x86_cpu_id array. Additionally, add a comment to the
> X86_BUG_MONITOR consumption site to make it clear how and why affected
> CPUs get IPIs to wake them up.
> 
> There is no equivalent erratum for the "Xeon D" Ice Lakes so
> INTEL_ICELAKE_D is not affected.
> 
> The erratum is called ICX143 in the "3rd Gen Intel Xeon Scalable
> Processors, Codename Ice Lake Specification Update". It is Intel
> document 637780, currently available here:
> 
> 	https://cdrdv2.intel.com/v1/dl/getContent/637780
> 
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Andrew Cooper <andrew.cooper3@...rix.com>
> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Cc: Len Brown <len.brown@...el.com>
> Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: stable@...r.kernel.org
> 
> ---
> 
>  b/arch/x86/include/asm/mwait.h |    3 +++
>  b/arch/x86/kernel/cpu/intel.c  |   17 ++++++++++++++---
>  2 files changed, 17 insertions(+), 3 deletions(-)
> 
> diff -puN arch/x86/kernel/cpu/intel.c~ICX-MONITOR-bug arch/x86/kernel/cpu/intel.c
> --- a/arch/x86/kernel/cpu/intel.c~ICX-MONITOR-bug	2025-04-18 13:54:46.022590596 -0700
> +++ b/arch/x86/kernel/cpu/intel.c	2025-04-18 15:15:19.374365069 -0700
> @@ -513,6 +513,19 @@ static void init_intel_misc_features(str
>  }
>  
>  /*
> + * These CPUs have buggy MWAIT/MONITOR implementations that
> + * usually manifest as hangs or stalls at boot.
> + */
> +#define MWAIT_VFM(_vfm)	\
> +	X86_MATCH_VFM_FEATURE(_vfm, X86_FEATURE_MWAIT, 0)
> +static const struct x86_cpu_id monitor_bug_list[] = {
> +	MWAIT_VFM(INTEL_ATOM_GOLDMONT),
> +	MWAIT_VFM(INTEL_LUNARLAKE_M),
> +	MWAIT_VFM(INTEL_ICELAKE_X),	/* Erratum ICX143 */
> +	{},
> +};

While it's just an internal helper, macro names should still be 
intuitive:

  s/MWAIT_VFM
   /VFM_MWAIT_BUG

or so?

Thanks,

	Ingo