Re: [PATCH] x86/hvm: Provide list of emulated features in HVM CPUID leaf

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 02/02/2016 06:22 PM, Andrew Cooper wrote:
> On 02/02/2016 23:17, Boris Ostrovsky wrote:
>> Hypervisor may choose which features to emulate for HVMlite guests.
>> Guest will query the HVM CPUID leaf to find out what is available.
>>
>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Roger also submitted a patch to do this.  However, it is not
> appropriate, so was dropped.
>
> An HVMLite domain should assume there are no emulated devices.  The very
> old legacy devices will never be implemented, and any others we care
> about possibly implementing in the future have APCI-based ways of
> indicating support.

OK, so I wasn't the first one to come up with this ;-)

I think for now I mostly care about APIC and for that I can use HW CPUID 
bit (which I believe is cleared for HVMlite guests). The trouble is that 
I need to present Linux as having APIC (boot code doesn't feel good if 
!cpu_has_apic) so I'll need to keep no-APIC emulation private to 
Xen-related code. Which is doable.

-boris