linux-kernel - Re: [tip: x86/urgent] x86/cpu: Fix AMD erratum #1485 on Zen4-based CPUs

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Message-ID: <ZScTem8iF8CUZqf6@gmail.com>
Date:   Wed, 11 Oct 2023 23:28:26 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     linux-tip-commits@...r.kernel.org, rene@...ctcode.de,
        "Borislav Petkov (AMD)" <bp@...en8.de>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [tip: x86/urgent] x86/cpu: Fix AMD erratum #1485 on Zen4-based
 CPUs


* tip-bot2 for Borislav Petkov (AMD) <tip-bot2@...utronix.de> wrote:

>  /* AMD Last Branch Record MSRs */
>  #define MSR_AMD64_LBR_SELECT			0xc000010e
>  
> +/* Zen4 */
> +#define MSR_ZEN4_BP_CFG			0xc001102e
> +#define MSR_ZEN4_BP_CFG_SHARED_BTB_FIX_BIT 5
>  
> +/* Zen 2 */
>  #define MSR_ZEN2_SPECTRAL_CHICKEN	0xc00110e3
>  #define MSR_ZEN2_SPECTRAL_CHICKEN_BIT	BIT_ULL(1)
>  
> +/* Fam 17h MSRs */
> +#define MSR_F17H_IRPERF			0xc00000e9

Yeah, so these latest AMD MSR definitions in <asm/msr-index.h> are pretty 
confused, they list MSRs in the following order:

   Zen 4
   Zen 2
   Fam 19h         // resolution in tip:master
   Fam 17h

where perf/core added a Fam 19h section a couple of days ago ...

While in reality:

   Zen 2 == Fam 17h
   Zen 4 == Fam 19h

So it's confusing to list these separately and out of order.

So in resolving the conflict in perf/core I updated this section to read:

  /* Fam 19h (Zen 4) MSRs */
  #define MSR_F19H_UMC_PERF_CTL		0xc0010800
  #define MSR_F19H_UMC_PERF_CTR		0xc0010801

  #define MSR_ZEN4_BP_CFG		0xc001102e
  #define MSR_ZEN4_BP_CFG_SHARED_BTB_FIX_BIT 5

  /* Fam 17h (Zen 2) MSRs */
  #define MSR_F17H_IRPERF		0xc00000e9

  #define MSR_ZEN2_SPECTRAL_CHICKEN	0xc00110e3
  #define MSR_ZEN2_SPECTRAL_CHICKEN_BIT	BIT_ULL(1)

This doesn't change the definitions themselves, only merges the comments 
and the sections, (to keep the Git conflict resolution non-evil), but 
arguably once perf/core goes upstream, we should probably unify the naming 
to follow the existing nomenclature, which is, starting at around F15H, the 
following:

   MSR_F15H_
   MSR_F16H_
   MSR_F17H_
   MSR_F19H_

Or are the MSRs named ZEN2 and ZEN4 in AMD SDMs, which we should follow?

Anyway, something to keep in mind.

Thanks,

	Ingo