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Date:   Tue, 18 Feb 2020 21:02:00 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     "Luck, Tony" <tony.luck@intel.com>
Cc:     Borislav Petkov <bp@alien8.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        Andy Lutomirski <luto@kernel.org>, x86-ml <x86@kernel.org>,
        lkml <linux-kernel@vger.kernel.org>
Subject: Re: [RFC] #MC mess
Message-ID: <20200218200200.GE11457@worktop.programming.kicks-ass.net>
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 <3908561D78D1C84285E8C5FCA982C28F7F57B937@ORSMSX115.amr.corp.intel.com>
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On Tue, Feb 18, 2020 at 06:20:38PM +0000, Luck, Tony wrote:
> > Anything else I'm missing? It is likely...
> 
> +	hw_breakpoint_disable();
> +	static_key_disable(&__tracepoint_read_msr.key);
> +	tracing_off();
> +
>  	ist_enter(regs);
> 
> How about some code to turn all those back on for a recoverable (where we actually recovered) #MC?

Then please rewrite the #MC entry code to deal with nested exceptions
unmasking the MCE, very similr to NMI.

The moment you allow tracing, jump_labels or anything else you can
expect #PF, #BP and probably #DB while inside #MC, those will then IRET
and re-enable the #MC.

The current situation is completely and utterly buggered.