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Re: [Xen-devel] Questions on EPT dump and creation

To: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Subject: Re: [Xen-devel] Questions on EPT dump and creation
From: YAO <yffbrave@xxxxxxxxx>
Date: Fri, 22 Jul 2011 16:45:08 +0800
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Hi, Tim
Thanks for your reply, I reviewed my code and found some confusing things:
We know the p2m top-level page is allocated in function "p2m_alloc_table" which called p2m_alloc_ptp, 
then the eptp can be assigned to point to this page.
An example looks like "mfn of page = 0xd4ec2, eptp = 0xd4ec201e" (I have 4G mem, Xen is 32bit PAE)

But when I allocate my p2m_top page, the mfn looks very strange----"mfn = 0x117b21".
I use "ept_set_middle_entry" to allocate pdp and get the mfn of pdp is "0x117b20". So is the case of allocating pd.

How could xen allocate a mfn beyond the total memory without any warning?
When I dump my page, I need to use map_domain_page. But it seems like I did map successfully using these mfn's.
That's puzzling.

Wait for your reply,

2011/7/20 Tim Deegan <Tim.Deegan@xxxxxxxxxx>
At 15:37 +0800 on 20 Jul (1311176224), YAO wrote:
> Many thanks for your tip, yes, I didn't cope with the levels properly. I
> have fixed it.
> But here's another problem. Since I have a full ept copy, if I replace the
> system eptp with my eptp,
> the domU will still be running like nothing happened. Now the domU may be
> compromised, it didn't response to any keystroke or click...
> Did I miss something when switching the eptp to and back?

Maybe?  This isn't the kind of bug I can fix by email; I think you need
to dig into it yourself.


Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, Xen Platform Team
Citrix Systems UK Ltd.  (Company #02937203, SL9 0BG)

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