[save/restore] Page types errors

[Jean-Yves Migeon <jean-yves.migeon%espci.fr@localhost>]

Hi list,

While making progress for the suspend/resume for a domU (I am able to 
erratically suspend and resume back to console, when disabling some 
xentools checks), I am experiencing difficulties during save/restore 
operation for page tables. I've been banging my head for two days on it 
now, and not able to identify where these errors may come from.

Just to illustrate my problem better (see my explanations below), here's 
a typical xm dmesg output during a save (there are many lines, just 
copy/pasting the relevant ones for this mail):

...
(XEN) mm.c:649:d0 Error getting mfn 1eeb0 (pfn 6f5) from L1 entry 
1eeb0003 for dom1
(XEN) mm.c:1833:d0 Bad type (saw 28000001 != exp e0000000) for mfn 1ee5b 
(pfn 74a)
(XEN) mm.c:649:d0 Error getting mfn 1ee5b (pfn 74a) from L1 entry 
1ee5b003 for dom1
(XEN) mm.c:1833:d0 Bad type (saw 58000001 != exp e0000000) for mfn 1ee3a 
(pfn 76b)
(XEN) mm.c:649:d0 Error getting mfn 1ee3a (pfn 76b) from L1 entry 
1ee3a003 for dom1
(XEN) mm.c:1833:d0 Bad type (saw 28000001 != exp e0000000) for mfn 1ed18 
(pfn 88d)
(XEN) mm.c:649:d0 Error getting mfn 1ed18 (pfn 88d) from L1 entry 
1ed18003 for dom1
(XEN) mm.c:1833:d0 Bad type (saw 28000001 != exp e0000000) for mfn 1ed16 
(pfn 88f)
...

When restoring, xend stops the operation when he encounters an error 
related to PD/PT:

[2008-06-12 14:50:09 211] INFO (XendCheckpoint:370) Reloading memory 
pages:   0%
[2008-06-12 14:50:09 211] INFO (XendCheckpoint:370) Received all pages 
(0 races)
[2008-06-12 14:50:09 211] INFO (XendCheckpoint:3100%
[2008-06-12 14:50:09 211] INFO (XendCheckpoint:370) Memory reloaded 
(3797 pages)
[2008-06-12 14:50:09 211] INFO (XendCheckpoint:370) ERROR Internal 
error: PT base is b
ad. pfn=1899 nr=3840 type=00000000 20000000
[2008-06-12 14:50:09 211] INFO (XendCheckpoint:370) Restore exit with rc=1
[2008-06-12 14:50:09 211] DEBUG (XendDomainInfo:1779) 
XendDomainInfo.destroy: domid=3
[2008-06-12 14:50:09 211] DEBUG (XendDomainInfo:1798) 
XendDomainInfo.destroyDomain(3)
[2008-06-12 14:50:09 211] ERROR (XendDomainInfo:1809) 
XendDomainInfo.destroy: xc.domai
n_destroy failed.

Here, we have an error related to a PT, for pfn 1899 (76b in hex), which 
you can identify in the xm dmesg output (which let me think that the 
problem is same for both errors).

Now, what I found this far: it happens after restoring the domain 
context (same as a dump-core operation), when xentools restore PD/PT 
(VM) mappings of the domain, and makes a couple of checks on it (Xen is 
tracking page types).

According to xen kernel sources, the types would translate as follow 
(see in include/asm-x86/mm.h):
28000001: L2 page, pinned
58000001: GDT page, pinned
e0000000: writable page, not pinned

Question is: Xen is expecting this pages to be writable ones, and found 
them as L2 page or GDT pages, pinned by guest. Before looking deeper 
into pmap, anybody knows if there's port-xen's code which could result 
in such warnings? Or am I mistaken?

Thanking you in advance for your help,

Cheers,

--
Jean-Yves Migeon
jean-yves.migeon%espci.fr@localhost