Re: [Xen-devel] [PATCH v2 0/4] Expose HW APIC virtualization support to HVM guests

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 03/11/2014 03:37 AM, Zhang, Yang Z wrote:
> Boris Ostrovsky wrote on 2014-03-11:
> > Version 2:
> > * Added ability to specify hypervisor CPUID leaves in config file (this requires
> >    new sysctl)
> > * Use 2 bits to indicate what is supported --- one for APIC memory access and
> > the
> >    other for x2APIC. Still not sure whether virtual interrupt delivery should be
> >    exposed as well.
> >
> > ...
> >
> > I am also not sure whether (cpu_has_vmx_apic_reg_virt &
> > cpu_has_vmx_virtualize_x2apic_mode) is sufficient to declare full HW
> > APIC support to a guest. The tests show ~95K VMEXITs when virtual
> The former is enough. Hardware has APICv must have the virtualize x2apic too.
>
> > interrupt delivery and posted interrupts are turned off so there
> > appears to still be some benefit. I suppose we can use another CPUID
> > bit for these two (although I am not particularly eager to do this).
> The three features are coexisting. I think you can use one bit to show them.
As I learned yesterday (the hard way) this is not necessarily the case. 
I was testing this on a laptop that has MSR 0x48b 
(MSR_IA32_VMX_PROCBASED_CTLS2) return 0x8ff00000000: yes for x2APIC 
virtualization but no for APIC register access virtualization.
Which is why I added another bit to distinguish the two


Thanks.
-boris


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