Re: [Xen-devel] [PATCH v9 1/3] xen/libxc: Allow changing max number of hypervisor cpuid leaves

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 04/23/2014 08:36 PM, Zhang, Yang Z wrote:
> Jan Beulich wrote on 2014-04-23:
> > I'll definitely want a VMX maintainer's ack (or at least Yang's 
> > consent) on patch 3 before applying the whole series (the first two 
> > patches alone don't make that much sense). 
> I have discussed with Boris before (offlist) and I don't think it is necessary 
> to expose two bits. Per my understanding, only one bit to indicate whether 
> APICv is enabled should be enough. The reason is that all hardwires that 
> support APICv must also support virtualized x2apic(Intel SDM doesn't say it 
> explicitly, but I get confirmed from hardware guys). And in current Xen's 
> implementation, it will enable APICv and virtualize_x2apic unconditionally if 
> hardware support them and not disabled by user. So based on current xen's 
> implementation, APICv is enabled means virtulized x2apic is enabled, vice 
> versa. That's the reason why I think one bit is enough.
> But if you guys think two bits also is acceptable, I am ok.

Jan, how do you want to proceed? Although I didn't realize that x2apic 
virtualization is guaranteed for APICv-enabled silicon I still prefer to 
keep separate bits for x2apic vs plain APIC for guests that can only use 
the latter.
(I know that I need to resend this in any case with stray printk removed)

-boris


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