linux-kernel - RE: [Patch V0] x86, mce: Ensure offline CPU's don't participate in mce rendezvous process.

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Date:	Fri, 4 Dec 2015 18:30:39 +0000
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Borislav Petkov <bp@...en8.de>
CC:	"Raj, Ashok" <ashok.raj@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
	"Andy Lutomirski (luto@...capital.net)" <luto@...capital.net>
Subject: RE: [Patch V0] x86, mce: Ensure offline CPU's don't participate in
 mce rendezvous process.

> Whether it is kosher or not is beside the point. Why should an offlined
> CPU even noodle through all that code if it doesn't need/have to? It can
> return immediately instead.

Ashok wants to move in stage 2 to having the offline cpu scan banks and report
any errors seen there.  To do that we'll have to run through a fair bit of the
do_machine_check() code.

But ... if you want a super safe version to put the stable tag on ... we could
just have something like this at the head of do_machine_check()

	int cpu = smp_processor_id();

	if (cpu_is_offline(cpu)) {
		rdmsr(MCG_STATUS);
		if (RIPV bit set) {
			wrmsr(MCG_STATUS, 0);
			return;
		}
		// can we do anything here? Offline cpu has no place to return to.
		// There are no good answers ... falling into the regular code is
		// what we did historically
	}

-Tony