[Xen-devel] page fault in shadow page-table

["Wu Bingzheng" <wubingzheng@xxxxxxx>]

Hi,

I am reading shadow memory code in Xen 3.3.0, and have a question.

In HVM guest, if a process writes a non-existing page, what happens:
First, page fault occurs, and traps into Xen. Xen finds out that that page doesn't exist in guest page table, so go back to guest.
The guest fixes this fault in its page table, and writes that page again. Because that page doesn't exist in shadow page table, so another page fault occurs, and traps into Xen again.
Xen finds out it's shadow page fault this time, so it fix this fault in shadow page table, and then go back to guest.
At last, the guest writes that page successfully.

Am I write? 
But in debug, I find out that, there are 3 page faults occurs in fact, the first 2 are guest page fault, and the last one is shadow page fault. 

What step do I miss?

Thanks,
Wu

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