From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jan Kiszka <jan.kiszka@web.de>
Subject: Re: VMX: Host NMI triggering on NMI vmexit
Date: Sat, 20 Sep 2008 08:55:55 +0200
Message-ID: <48D49E7B.9030606@web.de>
References: <48CF97F1.9090004@siemens.com> <48D429B1.6090105@redhat.com>
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Cc: "Yang, Sheng" <sheng.yang@intel.com>,
	kvm-devel <kvm@vger.kernel.org>
To: Avi Kivity <avi@redhat.com>
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Avi Kivity wrote:
> Jan Kiszka wrote:
>> Sheng,
>>
>> out of curiosity: vmx_vcpu_run invokes 'int $2' to trigger a host NMI =
if
>> the VM exited due to an external NMI event. According to Intel specs I=

>> have, software-triggered NMIs do not block hardware NMIs. So are we
>> facing the risk to receive another NMI while running the first handler=
?
>> Or will the VM be left with the hardware blocking logic armed? Or does=

>> Linux not care about NMI handler re-entrance?
>>  =20
>=20
> All good questions.  Usually this doesn't happen since NMI sources are
> far apart (oprofile, watchdog).

Only true until you have multiple unsynchronized NMI sources, e.g.
inter-CPU NMIs of kgdb + a watchdog. I just stumbled over several bugs
in kvm's and my own NMI code that were triggered by such a scenario
(sigh...).

>=20
> Maybe the answer is to generate the local nmi via an IPI-to-self comman=
d
> to the local apic.
>=20

That sounds like a good idea, will look into this right after fixing the
other NMI issues.

Jan


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