Re: [Xen-devel] [PATCH] x86: allow NMI injection

To:	Jan Beulich <jbeulich@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject:	Re: [Xen-devel] [PATCH] x86: allow NMI injection
From:	Keir Fraser <keir@xxxxxxxxxxxxx>
Date:	Wed, 28 Feb 2007 11:59:58 +0000
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On 28/2/07 11:39, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

> NetWare's internal debugger needs the ability to send NMI IPIs, and
> there is no reason to not allow domUs or dom0's vCPUs other than vCPU 0
> to handle NMIs (they just will never see hardware generated ones).
> 
> While currently not having a frontend, the added hypercall also allows
> for being used to inject NMIs into foreign VMs.
> 
> Along the lines, this fixes a potential race condition caused by
> previously accessing the VCPU flags field non-atomically in entry.S.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

Notably this patch changes the way that a NMI handler is registered to use
the native-like vector 2. This changes the guest interface though. Do you
really need to be able to specify a custom CS? Can you not vector to the
flat CS and then far jump?

I'm not sure about making the IPI function a physdev_op(), since this is
still a virtual NMI (it has nothing to do with real hardware NMIs). It might
be better to make it a vcpu_op. Then it would not be a great fit to allow
send-to-all send-to-all-butself overrides, but I'm not sure how important
that optimisation is (or is to make the NMI deliveries as simultaneous as
possible)?

 -- Keir

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