[Xen-devel] Creating guest with less than 4MB RAM causes Xen to crash immediately

[Wei Liu <Wei.Liu2@xxxxxxxxxx>]

Keir, Tim and IanJ

When user creates a guest with less than 4MB of memory, Xen crashes
immediately. That's because:

      * libxc round up memory to 4MB and build page table for the guest,
        see xc_dom_x86.c:count_pgtables. So the virt_pgtab_end is at
        least 0x400000.
      * When Xen try to pin page table for guest, it will scan through
        page table and invoke arch/x86/mm.c:get_page_type, which has a
        assertion that if any error happens the rc should only be
        -EINVAL, otherwise Xen crashes.
      * For a guest with less than 4MB memory, some of the entries in
        the page table are not valid, causing __get_page_type to fail
        with -EBUSY, which causes the assertion to fail.

In practice few people will create a DomU with less than 4MB ram. I
encounter this because I was trying to boot up ~3K+ minios.

Xen console log and xl output files attached.


Wei.

Attachment: mini-2m-crashed-xen.log
Description: Text Data

Attachment: mini-2m-crashed-xen-xl.log
Description: Text Data

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