Re: [Xen-devel] [PATCH] xen/apic: implement io apic read withhypercall

From: Ian Campbell
Date: Fri Apr 20 2012 - 09:12:46 EST

On Fri, 2012-04-20 at 13:53 +0100, Andrew Cooper wrote:
> >
> > Under what circumstances can these hypercalls fail? Would a BUG_ON be
> > appropriate/
> -EFAULT, -EPERM, anything xsm_apic() could return (which looks only to
> be -EPERM).

So either the guest has called a hypercall which it is not permitted to
or it has called it with invalid parameters of one sort or another. Both
of these would be a code bug in the guest and therefore asserting that
no failure occurred is reasonable?

What could the caller do with the error other than log it and collapse?

> The call into Xen itself will return 0 as a value if an
> invalid physbase is passed in the hypercall.

> So a BUG_ON() is not safe/sensible for domU.

I think you have successfully argued that it is ;-)


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