Re: [Xen-devel] live migration question

[Keir Fraser <keir@xxxxxxx>]

On 31/01/2012 12:42, "Juergen Gross" <juergen.gross@xxxxxxxxxxxxxx> wrote:

>> I've made an additional test using xm save/xm restore to see if the same
>> problem shows up. It does NOT. Mapping succeeds at once while restoring
>> memory is still running. I always thought xm restore and live migration on
>> the target machine are more or less the same. This seems not to be true.
> 
> Okay, here are my results (so far):
> 
> do_mmu_update() calls mod_l1_entry() which fails with -EINVAL due to an
> invalid mfn and p2m-type == 4 returned by:
> 
> mfn_x(gfn_to_mfn(pg_dom, l1e_get_pfn(nl1e), &p2mt))
> 
> I still don't see why xc_restore is able to do the mapping while my daemon is
> not. And I can't find any difference between a domain creation due to
> xm restore and a live migration.

Memory pages are populated as they appear in the migration data stream.
Perhaps you are trying to map a guest page that has simply not yet been
allocated.

Bear in mind that IOCTL_PRIVCMD_MMAPBATCH_V2 will note, but proceed past,
failed individual mappings. While IOCTL_PRIVCMD_MMAP, for example, will fail
the entire ioctl() in that situation. There's a reason that xc_restore uses
the former ioctl!

 -- Keir



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