From: Avi Kivity <avi@qumranet.com>
To: Jan Kiszka <jan.kiszka@web.de>
Cc: "Yang, Sheng" <sheng.yang@intel.com>, kvm-devel <kvm@vger.kernel.org>
Subject: Re: VMX: NMI injection without virtual NMI support
Date: Sat, 13 Sep 2008 11:58:33 +0300 [thread overview]
Message-ID: <48CB80B9.10201@qumranet.com> (raw)
In-Reply-To: <48CB5D3E.1000505@web.de>
Jan Kiszka wrote:
>> In some cases misbehaving NMIs are worse than no NMIs. For example, a
>> software watchdog may use NMIs to monitor a system. But if the guest
>> spins with interrupts disabled, the irq window will never open, and NMIs
>> will never be delivered, so the watchdog will deliver a false negative.
>>
>>
>
> I fail to see the regression. Currently that watchdog would _always_
> deliver false positives and pull the trigger immediately (in fact, this
> is precisely the situation we face @work with some special board
> emulation where we have to provide an NMI-based watchdog).
>
>
Linux checks whether nmi works and enables it only if it does (I think
-- not sure). So for Linux, there would be a regression.
> Moreover, only the second and succeeding NMIs under the same
> interrupts-disabled window need to get lost: Along with injecting the
> first NMI we could request the IRQ window unconditionally, using it to
> reset the virtual NMI-blocked state.
>
But the interrupt window would never open. Consider a spin_lock()
executing with interrupts disabled, on a spin lock that is already
locked by the current cpu.
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
prev parent reply other threads:[~2008-09-13 9:01 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-09-11 15:11 VMX: NMI injection without virtual NMI support Jan Kiszka
2008-09-12 6:29 ` Yang, Sheng
2008-09-12 8:34 ` Jan Kiszka
2008-09-13 5:14 ` Avi Kivity
2008-09-13 6:27 ` Jan Kiszka
2008-09-13 8:58 ` Avi Kivity [this message]
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