Jeremy, thanks for clarification, but I still not sure about following code in 
pv_ops dom0. Since the Local APIC is owned by Xen totally, why is it not 
"outright forbidden for the guest"?
 if (!xen_initial_domain())
 cpuid_leaf1_edx_mask &=
 ~((1 << X86_FEATURE_APIC) | /* disable local APIC */
 (1 << X86_FEATURE_ACPI)); /* disable ACPI */
Thanks
Yunhong Jiang
Jeremy Fitzhardinge wrote:
> On 07/28/09 20:19, Jiang, Yunhong wrote:
>> I have a question to xen_cpuid() in pv_ops guest. Currently
> the cpuid will be trapped to xen HV for emulation. So why do
> we still use cpuid_leaf1_edx_mask/cpuid_leaf1_ecx_mask to do
> mask in guest side? Havn't that been achieved in hypervisor already?
>> 
>
> Not entirely, or consistently. In general Xen masks features which
> are outright forbidden for the guest to use, but leaves things that
> might possibly be useful - we still need to mask those out. It also
> fails to mask some newer features which are not usable in guests
> (like GByte pages and XSAVE), so we need to mask those anyway. For
> domU, 
> the set of
> mask flags is under the control of the domain config file; a
> misconfiguration could enable flags that the kernel can simply not
> use. 
>
> J
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