linux-kernel - Re: [PATCH v2 1/2] x86/mce/AMD: Redo use of SMCA MCA

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Date:   Wed, 5 Apr 2017 15:39:42 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Yazen Ghannam <Yazen.Ghannam@....com>
Cc:     linux-edac@...r.kernel.org, Tony Luck <tony.luck@...el.com>,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] x86/mce/AMD: Redo use of SMCA MCA_DE{STAT,ADDR}
 registers

On Tue, Apr 04, 2017 at 12:24:31PM -0500, Yazen Ghannam wrote:
> From: Yazen Ghannam <yazen.ghannam@....com>
> 
> We have support for the new SMCA MCA_DE{STAT,ADDR} registers in Linux. So
> we've used these registers in place of MCA_{STATUS,ADDR} on SMCA systems.
> However, the guidance for current implementations of SMCA is to continue
> using MCA_{STATUS,ADDR} and to use MCA_DE{STAT,ADDR} only if a Deferred
> error was not found in the former registers. This also means we shouldn't
> clear MCA_CONFIG[LogDeferredInMcaStat].

Does that mean we should trust what BIOS has set it to?

> 
> Redo the AMD Deferred error interrupt handler to follow the guidance for
> current SMCA systems. Also, don't break after finding the first error.
> 
> Rework __log_error() for clarity.
> 
> Don't clear MCA_CONFIG[LogDeferredInMcaStat] during AMD mcheck init.
> 
> Signed-off-by: Yazen Ghannam <yazen.ghannam@....com>
> ---

...

> @@ -832,25 +821,29 @@ asmlinkage __visible void __irq_entry smp_trace_deferred_error_interrupt(void)
>  	exiting_ack_irq();
>  }
>  
> +static inline bool is_deferred_error(u64 status)
> +{
> +	return ((status & MCI_STATUS_VAL) && (status & MCI_STATUS_DEFERRED));
> +}
> +
>  /* APIC interrupt handler for deferred errors */
>  static void amd_deferred_error_interrupt(void)
>  {
>  	unsigned int bank;
> -	u32 msr_status;
>  	u64 status;
>  
>  	for (bank = 0; bank < mca_cfg.banks; ++bank) {
> -		msr_status = (mce_flags.smca) ? MSR_AMD64_SMCA_MCx_DESTAT(bank)
> -					      : msr_ops.status(bank);
> +		rdmsrl(msr_ops.status(bank), status);
>  
> -		rdmsrl(msr_status, status);
> +		if (is_deferred_error(status)) {
> +			__log_error_deferred(bank, false);
>  
> -		if (!(status & MCI_STATUS_VAL) ||
> -		    !(status & MCI_STATUS_DEFERRED))
> -			continue;
> +		} else if (mce_flags.smca) {
> +			rdmsrl(MSR_AMD64_SMCA_MCx_DESTAT(bank), status);
>  
> -		__log_error(bank, true, false, 0);
> -		break;
> +			if (is_deferred_error(status))
> +				__log_error_deferred(bank, true);
> +		}

The diff is very hard to parse, lemme paste the whole resulting function
after the patch:

> /* APIC interrupt handler for deferred errors */
> static void amd_deferred_error_interrupt(void)
> {
>         unsigned int bank;
>         u64 status;
> 
>         for (bank = 0; bank < mca_cfg.banks; ++bank) {
>                 rdmsrl(msr_ops.status(bank), status);
> 
>                 if (is_deferred_error(status)) {
>                         __log_error_deferred(bank, false);
> 
>                 } else if (mce_flags.smca) {
>                         rdmsrl(MSR_AMD64_SMCA_MCx_DESTAT(bank), status);
> 
>                         if (is_deferred_error(status))
>                                 __log_error_deferred(bank, true);

So this doesn't sound like the guidance: if we should fallback to the
DE* versions only if a deferred error wasn't found in the usual regs,
the logic should be:

static void __log_error_deferred(unsigned int bank)
{
	u32 msr_stat = msr_ops.status(bank);
	u32 msr_addr = msr_ops.addr(bank);

	/*
	 * __log_error() needs to return true to say it has logged successfully or false
	 * if it hasn't.
	 */
	if (__log_error(bank, msr_stat, msr_addr, 0))
		goto out;

	if (!mce_flags.smca)
		return;

	/*
	 * Couldn't log a deferred error from the usual regs, fallback to DE*
	 * variants.
	 */
        msr_stat = MSR_AMD64_SMCA_MCx_DESTAT(bank);
        msr_addr = MSR_AMD64_SMCA_MCx_DEADDR(bank);

        __log_error(bank, msr_stat, msr_addr, 0);

out:
        /* We should still clear MCA_DESTAT even if we used MCA_STATUS. */
        if (mce_flags.smca)
                wrmsrl(MSR_AMD64_SMCA_MCx_DESTAT(bank), 0);
}

and this way you don't need to wiggle around that use_smca_destat thing.

-- 
Regards/Gruss,
    Boris.

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