Why guest physical addresses are not the same as the corresponding host virtual addresses in QEMU/KVM? Thanks!

[harry harry <hiharryharryharry@gmail.com>]

Hi QEMU/KVM developers,

I am sorry if my email disturbs you. I did an experiment and found the
guest physical addresses (GPAs) are not the same as the corresponding
host virtual addresses (HVAs). I am curious about why; I think they
should be the same. I am very appreciated if you can give some
comments and suggestions about 1) why GPAs and HVAs are not the same
in the following experiment; 2) are there any better experiments to
look into the reasons? Any other comments/suggestions are also very
welcome. Thanks!

The experiment is like this: in a single vCPU VM, I ran a program
allocating and referencing lots of pages (e.g., 100*1024) and didn't
let the program terminate. Then, I checked the program's guest virtual
addresses (GVAs) and GPAs through parsing its pagemap and maps files
located at /proc/pid/pagemap and /proc/pid/maps, respectively. At
last, in the host OS, I checked the vCPU's pagemap and maps files to
find the program's HVAs and host physical addresses (HPAs); I actually
checked the new allocated physical pages in the host OS after the
program was executed in the guest OS.

With the above experiment, I found GPAs of the program are different
from its corresponding HVAs. BTW, Intel EPT and other related Intel
virtualization techniques were enabled.

Thanks,
Harry