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

[Superymk <superymkxen@xxxxxxxxxxx>]

So your point is the guest CR3 needs to be "extended" to 64 bits with 
zeroes first, if it is a 32-bit guest. right?
On 11/17/2010 6:11 PM, George Dunlap wrote:
> If you're in 64-bit mode and the hardware had a TLB miss for virtual
> address of 0xdeadb000, how would the hardware walk the pagetables?
> There are 20 bits for the virtual frame number, but each page-table
> entry has 9 bits.
>
> It's the exact same situation if the guest cr3 was set to 0xdeadb000.
> The indexes into the higher-level tables would simply be zero.
>
>   -George
>
> On Wed, Nov 17, 2010 at 9:40 AM, Superymk<superymkxen@xxxxxxxxxxx>  wrote:
> > Your figure points out the exactly EPT translation mechanism for an X64
> > guest.
> >
> > In the face of an X86_32 guest, how can EPT find the right EPML4 entry when
> > translating CR3's pfn value into the right mfn value? There are 20 bits for
> > indexing in total, while each level of EPT paging structure uses only 9 bits
> > for indexing.
> >
> >
> > On 11/17/2010 5:20 PM, Chu Rui wrote:
> >
> > Maybe this figure depicts the process...
> >
> > The original URL is http://software.intel.com/file/25040
> >
> > 2010/11/17 Superymk<superymkxen@xxxxxxxxxxx>
> > > Hi all,
> > >
> > > Can some one please tell me how EPT translates an X86_32 guest physical
> > > address? I have read the Intel's manual, but it seems there is no discussion
> > > about this condition.
> > >
> > > My concern is that, the guest CR3 pfn can be considered as being
> > > constituted by two 10 bits indexers for an X86_32 virtual machine. However,
> > > the EPT paging structures is similar with the page tables used on X86_64
> > > platform. which has four 9 bits indexers in its address layout. In addition,
> > > each EPT entry is 64 bits long. Hence, a 4K page can hold at most 512
> > > entries. So, if the guest CR3's pfn is 0xfffff (an X86_32 virtual machine)
> > > and I get a valid EPTP, how EPT will perform the translation?
> > >
> > > Thanks,
> > > Superymk
> > >
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