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Re: [Xen-devel] How EPT translates an X86_32 guest physical address?



Okay, in my mind, the hardware has only one work mode, 32bit or 64bit. Thus the 32bit guest address will be extended under the 64bit host.
But what will happen for a 64bit guest under a 32bit host :-)

2010/11/17 Ian Campbell <Ian.Campbell@xxxxxxxxxx>
On Wed, 2010-11-17 at 10:32 +0000, George Dunlap wrote:
> The exact implementation of 32-bit mode on a 64-bit capable processor
> is something only the engineers at Intel know; but logically yes,
> whatever it does is equivalent to first zero-extending the 32-bit
> value.

Even on x86_32 physical addresses are >32 bit (think PAE). cr3 is a
physical address, even if the register which exposes it happens to be
limited to 32 bits. cr3 has probably already been expanded to a full
physical address by the time EPT sees it and I don't think there's any
difference between 32 and 64 bit (at least in this aspect) in how EPT
handles the translation from physical address to machine address.

Ian.


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