linux-kernel - Re: [PATCH 2/3 V2] x86/mce: Fix incorrect "Machine check from unknown source" message

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Date:   Tue, 29 May 2018 11:54:25 -0700
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Borislav Petkov <bp@...e.de>
Cc:     "Williams, Dan J" <dan.j.williams@...el.com>,
        "Zhuo, Qiuxu" <qiuxu.zhuo@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3 V2] x86/mce: Fix incorrect "Machine check from
 unknown source" message

On Tue, May 29, 2018 at 07:53:14PM +0200, Borislav Petkov wrote:
> Nah, the cleanups will all go ontop. This is just a dirty branch to show
> my intention but yours go first and then the cleanup.

Couple of thoughts:

In "x86/mce: Carve out bank scanning code" you drop the extra
call to mce_severity() that I just added:

@@ -1310,10 +1318,8 @@ void do_machine_check(struct pt_regs *regs, long error_code)
 		 * fatal error. We call "mce_severity()" again to
 		 * make sure we have the right "msg".
 		 */
-		if (worst >= MCE_PANIC_SEVERITY && mca_cfg.tolerant < 3) {
-			severity = mce_severity(&m, cfg->tolerant, &msg, true);
+		if (worst >= MCE_PANIC_SEVERITY && mca_cfg.tolerant < 3)
 			mce_panic("Local fatal machine check!", &m, msg);
-		}
 	}

But "msg" won't have been filled in with the right message to match
the error in "m" (__mc_scan_banks() doesn't update "msg").

In "x86/mce: Exit properly when no banks to poll" you
leap right to the end.  I'm wondering whether this can
ever happen? I mean, if there are no machine check banks,
then how did we get a machine check?

Both the original, and your new code, skip the:

	mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);

which seems bad. That leaves MCG_STATUS.MCIP set ... so a second
machine check would just reset the machine.

-Tony

P.S. What happened to my "part 3/3" (updating the Skylake quirk)
... does that belong in somebody else's tree?