Re: Question about EPT translation

Re: Question about EPT translation

[Daniel Castro]

Hello,
Next time I will only replay through the list. CC the list

2011/5/29 henanwxr <henanwxr@hotmail.com>:
> Hi Daniel, I have post my questions on xen-devel but nobody reply. So I turn
> to you for help.
> 1. Does hvmoader need EPT for address translation when it  is running?
If you are talking to pure HVM Guest then yes.
> 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
> 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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| |   | Daniel Castro,                |
| |   | Consultant/Programmer.|
| |   | U Andes                         |
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Re: Re: Question about EPT translation

[Ian Campbell]

On Sun, 2011-05-29 at 22:49 +0100, Daniel Castro wrote:
> Hello,
> Next time I will only replay through the list. CC the list
> 
> 2011/5/29 henanwxr <henanwxr@hotmail.com>:
> > Hi Daniel, I have post my questions on xen-devel but nobody reply. So I turn
> > to you for help.

I also received private mail from this poster with pretty much identical
content. I replied privately at length on the inappropriateness of this
sort of behaviour but just to be extra clear: henanwxr -- it is not ever
appropriate to scatter-shot private mails to people when you do not get
an immediate reply to a list posting.

I recommend that people who receive such emails either ignore them or
ask them to be reposted on the list before replying, so as not to
encourage this way of thinking.

Ian.

Re: Re: Question about EPT translation

[Ian Campbell]

On Sun, 2011-05-29 at 22:49 +0100, Daniel Castro wrote:
> 2011/5/29 henanwxr <henanwxr@hotmail.com>:
> > 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.

Ian.