[vbox-dev] Arrangement of EPT structures with SMP

[Tom Birch]

So this means the value of EPTP on each vcpu is the same?

My question before was: how do they actually share the same page
table? Is the EPT pointer copied between VCPUs (either directly or
indirectly)? Can you point to the code that does this?

cheers,
Tom

On Thu, Oct 29, 2009 at 1:58 PM, Sander van Leeuwen
<Sander.Vanleeuwen at sun.com> wrote:
> Each VCPU has its own root page table, but all VCPUs are sharing the same
> one with EPT (or AMD nested paging for that matter).
>
> Tom Birch wrote:
>>
>> Cool, thanks, that's what I thought. Is there any reason the EPT is a
>> per-VCPU data structure? Could you please point me to the bits of code
>> that do this sharing? I'm getting lost looking at all the assignments
>> to the pShwPageCR3* variables, they still all seem to be per-VCPU, I
>> can't find where it hooks into the root VM structure.
>>
>> cheers,
>> Tom
>>
>> On Thu, Oct 29, 2009 at 1:19 PM, Sander van Leeuwen
>> <Sander.Vanleeuwen at sun.com> wrote:
>>
>>>
>>> The EPT structures are shared between all VCPUs as they contain a guest
>>> physical to host physical mapping, which
>>> is independent of the VCPU. The host OS is irrelevant.
>>>
>>> Tom Birch wrote:
>>>
>>>>
>>>> I'm looking through the page management code, specifically hardware
>>>> acceleration on Intel with EPT, and I can't quite figure out the
>>>> high-level relationships between various structures. Both the VMCS and
>>>> EPTP seem to be per-PVMCPU data structures, does this mean that within
>>>> a single VM, you can have multiple distinct EPTPs (on different
>>>> VCpus), or is this arrangement just a consequence of the way shadow
>>>> paging worked before EPT? Put another way, can I guarantee that all
>>>> VCpus within a single VM will all share the same EPTP? I'm mainly
>>>> concerned about how this applies to Darwin if that matters, but I
>>>> seems like a fairly Host-OS-agnostic feature.
>>>>
>>>> cheers,
>>>> Tom
>>>>
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>>>>
>>>>
>>>
>>> --
>>> Kind regards / Mit freundlichen Gruessen / Met vriendelijke groet
>>>
>>> --
>>>
>>> Sun Microsystems GmbH        Sander van Leeuwen
>>> Werkstrasse 24               Senior Staff Engineer, VirtualBox
>>> 71384 Weinstadt, Germany     mailto:Sander.Vanleeuwen at sun.com
>>>
>>>
>>> ================================================
>>> Sitz der Gesellschaft: Sun Microsystems GmbH,
>>> Sonnenallee 1, 85551 Kirchheim-Heimstetten
>>> Amtsgericht Muenchen: HRB 161028
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>>>
>>>
>
>
> --
> Kind regards / Mit freundlichen Gruessen / Met vriendelijke groet
>
> --
>
> Sun Microsystems GmbH        Sander van Leeuwen
> Werkstrasse 24               Senior Staff Engineer, VirtualBox
> 71384 Weinstadt, Germany     mailto:Sander.Vanleeuwen at sun.com
>
>
> ================================================
> Sitz der Gesellschaft: Sun Microsystems GmbH,
> Sonnenallee 1, 85551 Kirchheim-Heimstetten
> Amtsgericht Muenchen: HRB 161028
> Geschaeftsfuehrer: Thomas Schroeder,
> Wolfgang Engels, Dr. Roland Boehmer
> Vorsitzender des Aufsichtsrates: Martin Haering
> ================================================
>
>