[Xen-devel] the cause of invalid entries in physical-to-machine table

[Stephan Creutz <stephan.creutz@xxxxxxxxxxxxxxxxx>]

Hi,

I am currently trying to understand the details of live-migration by
looking at the code xc_linux_save.c in libxc and writing a simple
program to make things more clear.

The program memory maps all mfns which are used for the pfn to mfn list,
goes through all pfns, resolves each pfn to a mfn and tries to memory
map each of them to read its content. One thing I noticed are invalid
physical-to-machine list entries (list entries where the resulting mfn
equals INVALID_P2M_ENTRY and xc_map_foreign_range failes). I wonder what
are the possible causes for invalid entries in the pfn to mfn list. One
cause I can think of are pfns that are reserved for Xen itself, but what
are the other ones?

BTW: as far as I understand, xc_map_foreign_range should use the size 1
instead of PAGE_SIZE to get the shared info page and
live_p2m_frame_list_list because this function expects the size in
multiples of the page size not in bytes.

Stephan

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