linux-kernel - RE: [PATCHV2 2/3] x86, ras: Extend machine check recovery code to annotated ring0 areas

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Date:	Tue, 15 Dec 2015 23:46:03 +0000
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Borislav Petkov <bp@...en8.de>
CC:	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	"Williams, Dan J" <dan.j.williams@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-nvdimm@...1.01.org" <linux-nvdimm@...1.01.org>,
	"x86@...nel.org" <x86@...nel.org>
Subject: RE: [PATCHV2 2/3] x86, ras: Extend machine check recovery code to
 annotated ring0 areas

>> +	/* Fault was in recoverable area of the kernel */
>> +	if ((m.cs & 3) != 3 && worst == MCE_AR_SEVERITY)
>> +		if (!fixup_mcexception(regs, m.addr))
>> +			mce_panic("Failed kernel mode recovery", &m, NULL);
>				   ^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> Does that always imply a failed kernel mode recovery? I don't see
>
>	(m.cs == 0 and MCE_AR_SEVERITY)
>
> MCEs always meaning that a recovery should be attempted there. I think
> this should simply say
>
>	mce_panic("Fatal machine check on current CPU", &m, msg);

I don't think this can ever happen. If we were in kernel mode and decided
that the severity was AR_SEVERITY ... then search_mcexception_table()
found an entry for the IP where the machine check happened.

The only way for fixup_exception to fail is if search_mcexception_table()
now suddenly doesn't find the entry it found earlier.

But if this "can't happen" thing actually does happen ... I'd like the panic
message to be different from other mce_panic() so you'll know to blame
me.

Applied all the other suggestions.

-Tony