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[Xen-devel] Question about MMU update on HVM guest


I have some questions about MMU update operation.
I add some logging in function do_mmu_update (in file /xen/arch/x86/mm.c), and start Windows 7 32 bit HVM guest.
After guest started, I look at log and see that MMU update has been called with every page of guest, with pt_ower = 0 and pg_owner = 1. And with every page, MMU update called 2 times. The first time, page->count_info = 0x8000000000000002 after MMU update, but after that it decrease to 0x8000000000000001 in a different function. At the second time, page->count_info = 0x8000000000000002 after MMU update, and keep that value forever.

So the question is, why domain 0 have a reference to every pages of HVM guest ?
And why in the second time of MMU update, count_info doesn't decrease to 0x8000000000000001 ?

Thanks & Best Regards.

Nguyễn Ngọc Anh
Student - Course 53
Department of Computer Engineering - School of Information and Communication Technology 
Hanoi University Of Science And Technology.
Mobile: 0973402195
Email: ngocanh198@xxxxxxxxx
Y!M: pancuro
Skype: ngocanh19890
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