linux-kernel - Re: [Xen-devel] xen/x86: properly retrieve NMI reason

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Date:	Fri, 02 Jan 2015 15:55:11 +0000
From:	"Jan Beulich" <jbeulich@...e.com>
To:	<david.vrabel@...rix.com>, <boris.ostrovsky@...cle.com>,
	<konrad.wilk@...cle.com>
Cc:	<xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] xen/x86: properly retrieve NMI reason

>>> David Vrabel <david.vrabel@...rix.com> 12/23/14 12:01 PM >>>
>On 19/12/14 16:16, Jan Beulich wrote:
>> Using the native code here can't work properly, as the hypervisor would
>> normally have cleared the two reason bits by the time Dom0 gets to see
>> the NMI (if passed to it at all). There's a shared info field for this,
>> and there's an existing hook to use - just fit the two together. Note
>> that the hook can (and should) be used irrespective of whether being in
>> Dom0, as accessing port 0x61 in a DomU would be even worse, while the
>> shared info field would just hold zero all the time.
>
>What's the user visible impact of this fix?

Depends on what "user visible" is: It ought to prevent "Dazed and confused..."
messages when not really applicable, and allow to get forwarded particularly
SERR ones to APEI (GHES) code instead. I can't say I've seen this work in
practice, as I lack ways to force SERR on otherwise well behaving hardware,
but code inspection shows that the way it is now it can't work as intended.

Jan

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