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Message-ID: <1334927566.28331.80.camel@zakaz.uk.xensource.com>
Subject: Re: [Xen-devel] [PATCH] xen/apic: implement io apic read with
 hypercall
From: Ian Campbell <Ian.Campbell@citrix.com>
To: Andrew Cooper <Andrew.Cooper3@citrix.com>
CC: Lin Ming <mlin@ss.pku.edu.cn>,
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        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Date: Fri, 20 Apr 2012 14:12:46 +0100
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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 ;-)

Ian.