Re: [Xen-devel] xen: mm.c MFN errors

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2011-02-24 at 22:01 +0000, Shriram Rajagopalan wrote:
> I had this problem in 4.0.1 (still not resolved) and it persists in
> 4.1.0-rc6-pre.
>  And I am not the only one facing this issue apparently.
> http://lists.xensource.com/archives/html/xen-users/2011-02/msg00362.html
>  also reports the same issue, on xen 4.0.2-rc2
> 
> My workload was simple 2.6.18 domU (512M) with just 2 threads constantly
> mallocing, touching and freeing memory.
> 
> I enabled remus on the domain (just memory replication) which basically
> exercises xc_domain_save/xc_domain_restore paths.

What is your dom0 kernel version?

Does a basic save/restore or live migrate work in the same
configuration? e.g. "xm save"+"xm restore" or "xm migrate --live".

> Issue 1:
>  On primary during replication, xm dmesg logs are flooded with messages like
> ........
> (XEN) mm.c:889:d0 Error getting mfn 468900 (pfn 1fdd1) from L1 entry
> 8000000468900625 for l1e_owner=0, pg_owner=17

Dom0 failing to map a page owned by dom17? I'm not sure why that might
happen. I'd hazard that DOMID_SELF was getting used somewhere that the
foreign domain id was required, perhaps due to using an incorrect
interface (e.g. perhaps emulated pt updates instead of a hypercall).

My first instinct would be to dig into the MMAP_BATCH ioctl interfaces
in the privcmd driver.

> Issue 2:
>  VM fails to recover on secondary when I destroy it on primary. xm
> dmesg on secondary again shows issues wrt pagetable pinning
[...]

If dom0 is failing to map guest pages on the source domain then I think
all bets are off wrt getting something sane on the other end.

Ian.

> I wager this has got something to do either with the
> canonicalization/uncanonicalization code but cannot pin point
> where exactly, atm.
> shriram
> 
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