Re: Distinguishing gpfn, gmfn, mfn, and pfn

[Keir Fraser <keir.xen@gmail.com>]

On 29/05/2013 02:03, "Sengul Thomas" <thomas.sengul@gmail.com> wrote:

> Hi xen developers,
> 
> I'm confused about the actual usage of the four types of frames.
> I can find the definition in xen/include/xen/mm.h, but would like
> to check my understanding is correct:
> 
> 1) Is 2-stage MMU-supported (e.g., ARMv7 VE) translation
>     auto-translated mode? Then, gpfn == gmfn.
> 
> 2) Is gmfn --> mfn mapping the p2m table?
> 
> 3) Paravirtualized x86 guest will have gpfn != gmfn, and it is
>     quite hard to imagine. Could you tell me the difference
>     between gpfn and gmfn? (for instance, when it is used)

There are basically two modes:

 gmfn==gpfn: Guest does not see real machine physical addresses. p2m is done
by the hypervisor. This is like x86 HVM guests.
 gmfn==mfn: Guest does see real machine physical addresses. Typically the
guest will have its own concept of a flat pseudophysical address space that
it maps to real machine addresses with its own p2m table. This is like x86
pure PV guests.

ARM7 VE does indeed support HVM for ARM, and gmfn==gpfn.

 -- Keir

> 
> thanks always,
> Thomas
> 
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