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

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

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