Re: [Xen-devel] [PATCH V3] vmx/nmi: Do not use self_nmi() in VMEXIT handler

[Tim Deegan <tim@xxxxxxx>]

At 14:42 +0000 on 28 Feb (1362062542), Jan Beulich wrote:
> > +out:
> > +    enable_nmis();
> 
> ... this must not be done when on the NMI stack (i.e. when the
> NMI was raised while in hypervisor context).

Right; I had forgotten that we didn't switch stacks in that case. 

> Checking for this
> here would be strait forward, but I was really considering to do
> all of this in the assembly exit path, and I was still undecided
> whether we shouldn't follow Linux in skipping softirq processing
> (and hence scheduling) on the way out from an NMI (I don't
> think we'd need to do the same for MCE).

That sounds sensible, if it simplifies the logic (i.e. if it avoids
needing an extra IRET just to re-enable NMIs when we might as well IRET
to the guest).  Or is there any other reason to avoid it?

Tim.

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