linux-kernel - Re: [PATCH] x86/mce: Add workaround for SKX/CLX/CPX spurious machine checks

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Date:   Tue, 15 Feb 2022 10:42:42 -0800
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Jue Wang <juew@...gle.com>
Cc:     Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Subject: Re: [PATCH] x86/mce: Add workaround for SKX/CLX/CPX spurious machine
 checks

On Tue, Feb 08, 2022 at 07:09:45AM -0800, Jue Wang wrote:
> +static bool quirk_skylake_repmov(void)
> +{
> +	u64 mcgstatus = mce_rdmsrl(MSR_IA32_MCG_STATUS);
> +	u64 misc_enable = __rdmsr(MSR_IA32_MISC_ENABLE);
> +
> +	if ((mcgstatus & MCG_STATUS_LMCES) &&
> +	    unlikely(misc_enable & MSR_IA32_MISC_ENABLE_FAST_STRING)) {
> +		u64 mc1_status = mce_rdmsrl(MSR_IA32_MCx_STATUS(1));
> +

Needs a comment that this big blob of logic is checking for a software
recoverable data fetch error.

> +		if ((mc1_status &
> +		     (MCI_STATUS_VAL|MCI_STATUS_OVER|MCI_STATUS_UC|MCI_STATUS_EN|
> +		      MCI_STATUS_ADDRV|MCI_STATUS_MISCV|MCI_STATUS_PCC|
> +		      MCI_STATUS_AR|MCI_STATUS_S)) ==
> +		    (MCI_STATUS_VAL|MCI_STATUS_UC|MCI_STATUS_EN|MCI_STATUS_ADDRV|
> +		     MCI_STATUS_MISCV|MCI_STATUS_AR|MCI_STATUS_S)) {
> +			msr_clear_bit(MSR_IA32_MISC_ENABLE,
> +				      MSR_IA32_MISC_ENABLE_FAST_STRING_BIT);
> +			mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
> +			mce_wrmsrl(MSR_IA32_MCx_STATUS(1), 0);
> +			pr_err_once("Errata detected, disable fast string copy instructions.\n");
> +			return true;
> +		}
> +	}
> +	return false;
> +}

Otherwise:

Reviewed-by: Tony Luck <tony.luck@...el.com>

-Tony