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Re: [Xen-devel] Re: Question about EPT translation

To: Daniel Castro <evil.dani@xxxxxxxxx>
Subject: Re: [Xen-devel] Re: Question about EPT translation
From: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
Date: Tue, 31 May 2011 10:19:24 +0100
Cc: henanwxr <henanwxr@xxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On Sun, 2011-05-29 at 22:49 +0100, Daniel Castro wrote:
> 2011/5/29 henanwxr <henanwxr@xxxxxxxxxxx>:
> > 1. Does hvmoader need EPT for address translation when it  is running?
> If you are talking to pure HVM Guest then yes.

It doesn't have to be EPT (which is the name of an Intel specific
hardware technology). hvmloader needs some sort of page table
translation, which might be HAP (the generic name for both Intel's EPT
and AMD's nested paging) or shadow page tables depending on the hardware
capabilities your system has.

> > 2. I am sure the guest kernel need EPT when running, but not sure whether
> > hvmloader also needs. I think  when virtual bios in hvmloader running, we
> > should make virtual bios sees as if the memory starting from 0, so hvmloader
> > needs EPT, am I right?
> Yes

Again, correct modulo the above. hvmloader runs in the guest's context
and hence needs everything the guest kernel will need.

Actually in the case of hvmloader "needs" is rather a strong word, "runs
in that environment by design" would perhaps be more accurate.

> > 3. If hvmloader needs EPT, where we construct EPT structure for it? I can't
> > find correlative part  in code flow.
> The address translation is not done by hvmloader, hvmloader is only
> used to deploy data to memory, the translation is done via Hypervisor
> aided by hardware.


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