linux-kernel - Re: [RFC] #MC mess

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Message-ID: <20200218203404.GI11457@worktop.programming.kicks-ass.net>
Date:   Tue, 18 Feb 2020 21:34:04 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andy Lutomirski <luto@...nel.org>, x86-ml <x86@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] #MC mess

On Tue, Feb 18, 2020 at 08:11:10PM +0000, Luck, Tony wrote:
> > Then please rewrite the #MC entry code to deal with nested exceptions
> > unmasking the MCE, very similr to NMI.
> 
> #MC doesn't work like NMI.  It isn't enabled by IRET.  Nested #MC cause an
> immediate reset.  Detection of nested case is by IA32_MCG_STATUS.MCIP.
> We don't clear MCG_STATUS until we are ready to return from the machine
> check handler.

Ooh, excellent! That saves a whole heap of problems.

Then I suppose we should work at getting in_nmi() set. Let me have
another look at things.