linux-kernel - Re: [PATCH V2 1/1] x86/mce/amd: Add PPIN support for AMD MCE

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Message-ID: <20200321093850.GA17494@zn.tnic>
Date:   Sat, 21 Mar 2020 10:39:00 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Wei Huang <wei.huang2@....com>
Cc:     linux-kernel@...r.kernel.org, tony.luck@...el.com,
        yazen.ghannam@....com, tglx@...utronix.de, mingo@...hat.com,
        hpa@...or.com, linux-edac@...r.kernel.org, x86@...nel.org,
        smita.koralahallichannabasappa@....com
Subject: Re: [PATCH V2 1/1] x86/mce/amd: Add PPIN support for AMD MCE

On Fri, Mar 20, 2020 at 02:43:05PM -0500, Wei Huang wrote:
> Newer AMD CPUs support a feature called protected processor identification
> number (PPIN). This feature can be detected via CPUID_Fn80000008_EBX[23].
> However CPUID alone is not enough to read the processor serial number.
> MSR_AMD_PPIN_CTL also needs to be configured properly. If for any reason
> X86_FEATURE_AMD_PPIN[PPIN_EN] can not be turned on, such as disabled in
> BIOS, we have to clear the CPU capability bit of X86_FEATURE_AMD_PPIN.
> 
> When the X86_FEATURE_AMD_PPIN capability is available, MCE can read the
> serial number to keep track the source of MCE errors.
> 
> Co-developed-by: Smita Koralahalli Channabasappa <smita.koralahallichannabasappa@....com>
> Signed-off-by: Smita Koralahalli Channabasappa <smita.koralahallichannabasappa@....com>
> Signed-off-by: Wei Huang <wei.huang2@....com>
> Acked-by: Tony Luck <tony.luck@...el.com>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Yazen Ghannam <yazen.ghannam@....com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: linux-edac <linux-edac@...r.kernel.org>
> Cc: x86-ml <x86@...nel.org>
> ---
>  arch/x86/include/asm/cpufeatures.h |  1 +
>  arch/x86/kernel/cpu/amd.c          | 26 ++++++++++++++++++++++++++
>  arch/x86/kernel/cpu/mce/core.c     |  2 ++
>  3 files changed, 29 insertions(+)
> 
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index f3327cb56edf..4b263ffb793b 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -299,6 +299,7 @@
>  #define X86_FEATURE_AMD_IBRS		(13*32+14) /* "" Indirect Branch Restricted Speculation */
>  #define X86_FEATURE_AMD_STIBP		(13*32+15) /* "" Single Thread Indirect Branch Predictors */
>  #define X86_FEATURE_AMD_STIBP_ALWAYS_ON	(13*32+17) /* "" Single Thread Indirect Branch Predictors always-on preferred */
> +#define X86_FEATURE_AMD_PPIN		(13*32+23) /* Protected Processor Inventory Number */
>  #define X86_FEATURE_AMD_SSBD		(13*32+24) /* "" Speculative Store Bypass Disable */
>  #define X86_FEATURE_VIRT_SSBD		(13*32+25) /* Virtualized Speculative Store Bypass Disable */
>  #define X86_FEATURE_AMD_SSB_NO		(13*32+26) /* "" Speculative Store Bypass is fixed in hardware. */
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index 1f875fbe1384..9176db4be69b 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -394,6 +394,31 @@ static void amd_detect_cmp(struct cpuinfo_x86 *c)
>  	per_cpu(cpu_llc_id, cpu) = c->phys_proc_id;
>  }
>  
> +static void amd_detect_ppin(struct cpuinfo_x86 *c)
> +{
> +	unsigned long long val;
> +
> +	if (cpu_has(c, X86_FEATURE_AMD_PPIN)) {

Flip check:

	if (!cpu_has...
		return;

> +		/* Turn off now until MSR is properly configured */
> +		clear_cpu_cap(c, X86_FEATURE_AMD_PPIN);

What for? You can do the final decision in the end, once, instead of
toggling that bit here.

> +
> +		if (rdmsrl_safe(MSR_AMD_PPIN_CTL, &val))
> +			return;
> +
> +		if ((val & 3UL) == 1UL)
> +			return;
> +
> +		if (!(val & 2UL)) {
> +			wrmsrl_safe(MSR_AMD_PPIN_CTL,  val | 2UL);
> +			rdmsrl_safe(MSR_AMD_PPIN_CTL, &val);
> +		}

Those need comments what they do, like in the Intel variant.

> +
> +		/* MSR_AMD_PPIN_CTL[PPIN_EN] bit is 1, turn feature back on */
> +		if (val & 2UL)
> +			set_cpu_cap(c, X86_FEATURE_AMD_PPIN);

No, keep the feature bit set and clear it only when you determine so
instead of clearing and setting again.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette