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

From: Andrew Cooper
Date: Fri Apr 20 2012 - 09:20:19 EST

On 20/04/12 14:12, Ian Campbell wrote:
> 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.

So I have. -EMoreCoffee

Yes - I meant to say that BUG_ON() was ok for domU.

Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer
T: +44 (0)1223 225 900,

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