[Xen-devel] Re: nested virtualization: cpuid PSE36

[Tim Deegan <tim@xxxxxxx>]

cc-ing xen-devel.

Hi, 

At 13:51 +0200 on 09 Sep (1315576282), Christoph Egger wrote:
> I am trying to get Hyper-V up and running as l1 hypervisor.
> It claims the cpu does not provide the
> required feature: leaf 0x1, edx, bit 17 (= PSE36).

Huh.  Is this 32-bit Hyper-V?  If it's only needed for 32-bit then it's
not so important (32-bit Hyper-V is going away in Win8 anyway).  
I wonder if it's actually used - I guess if you don't need 4k protection
granularity for high mappings then it saves on pagetable space and TLB
pressure.

> Xen does indeed not propagate this feature bit to the l1 guest.
> 
> What do you think how should this be done to support this feature bit
> for the hap case?

I think that for HAP it would be enough to add support to the
guest_walk.c page walker (and gate the cpuid bit so we never advertise
it to shadow-paging guests).  It shouldn't be hard to add it to the
shadow pagetables either; it was just never needed before. 

Cheers,

Tim.

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