RE: [Xen-devel] PSE support in VT guests

["Nakajima, Jun" <jun.nakajima@xxxxxxxxx>]

Keir Fraser wrote:
> On 13 Jan 2006, at 19:26, Stephen Goglin wrote:
> 
>> As far as I can tell, Xen's approach to PSE support in VT guests is
>> it just doesn't expose the feature.  Is there any plan on adding
>> support for it?  Or is it already there and I am just missing
>> something? 
> 
> I think it's there already. After all, 64-bit OSes know the CPU will
> always support PSE.
> 
>   -- Keir
> 

That's correct. For 32-bit guests, we simply disable PSE at the CPUID
instruction. It's possible to turn it on (by extending the PSE
supporting code for 64-bit), but the current implementation of 2MB page
support is to fracture it into 4KB pages in the shadow page table, as we
don't have a generic 2MB page allocator in Xen (yet?). So in terms of
performance, we don't gain anything even if we enable PSE for 32-bit
guests.

Jun
---
Intel Open Source Technology Center

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