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

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@xxxxxxxxxx>
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.


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