linux-kernel - Re: [PATCH v7 2/8] x86/mce: Unify AMD DFR handler with MCA Polling

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Message-ID: <20251028174656.GBaQEBkOErfNAJbJsf@fat_crate.local>
Date: Tue, 28 Oct 2025 18:46:56 +0100
From: Borislav Petkov <bp@...en8.de>
To: Yazen Ghannam <yazen.ghannam@....com>
Cc: x86@...nel.org, Tony Luck <tony.luck@...el.com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>, linux-kernel@...r.kernel.org,
	linux-edac@...r.kernel.org, Smita.KoralahalliChannabasappa@....com,
	Qiuxu Zhuo <qiuxu.zhuo@...el.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	Bert Karwatzki <spasswolf@....de>, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v7 2/8] x86/mce: Unify AMD DFR handler with MCA Polling

On Tue, Oct 28, 2025 at 11:42:58AM -0400, Yazen Ghannam wrote:
> Yes, fair point. How about this?
> 
> 	/*
> 	 * If MCA_STATUS has a valid error of any type, then use it.
> 	 *
> 	 * If the error happens to be a deferred error, then the copy
> 	 * saved in MCA_DESTAT will be cleared at the end of the
> 	 * handler.
> 	 *
> 	 * If MCA_STATUS does not have a valid error, then check
> 	 * MCA_DESTAT for a valid deferred error.
> 	 */

Well, we already have this at the top:

/* 
 * We have three scenarios for checking for Deferred errors:
 * 
 * 1) Non-SMCA systems check MCA_STATUS and log error if found.
 * 2) SMCA systems check MCA_STATUS. If error is found then log it and also
 *    clear MCA_DESTAT.
 * 3) SMCA systems check MCA_DESTAT, if error was not found in MCA_STATUS, and
 *    log it.
 */

 and that is good enough IMO. The rest people can read out from the code.

> Okay, agreed. I think this entire second comment can be removed.

Gone.

IOW, this:

/* 
 * We have three scenarios for checking for Deferred errors:
 * 
 * 1) Non-SMCA systems check MCA_STATUS and log error if found.
 * 2) SMCA systems check MCA_STATUS. If error is found then log it and also
 *    clear MCA_DESTAT.
 * 3) SMCA systems check MCA_DESTAT, if error was not found in MCA_STATUS, and
 *    log it.
 */
static bool smca_should_log_poll_error(struct mce *m)
{
        if (m->status & MCI_STATUS_VAL)
                return true;
 
        m->status = mce_rdmsrq(MSR_AMD64_SMCA_MCx_DESTAT(m->bank));
        if ((m->status & MCI_STATUS_VAL) && (m->status & MCI_STATUS_DEFERRED)) {
                m->kflags |= MCE_CHECK_DFR_REGS;
                return true;
        }
 
        return false;
}

-- 
Regards/Gruss,
    Boris.

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