Xen users - Nov 2011 - Problem with dump-core after restoring machine

Hello, I have problem with dumping core of hvm domain. Problem occurs
only after previously restoring machine from a save file. There is no
problem with dumping core after creating domain from a scratch and then
trying to dump. Also there is no such problem with paravirtualized domains.

Error message I got (tried using both xm and xl):

xc: error: Failed to write buffer (14 = Bad address): Internal error
libxl: error: libxl.c:479:libxl_domain_core_dump core dumping domain 14
to ./dump.2: Bad address
core dump failed (rc=-3)

and using xm:

Fault 2: "Failed to dump core: (1, ''Internal error'',
''Failed to write
buffer (14 = Bad address)'')"


My dom0 is Debian Squeeze with Xen 4.1 and kernel 3.0, but also tried
with Xen 4.0 and 2.6.32 kernel. HVM domain is Windows XP (tried 32 and
64 bit).

I''d like to know if this is more general problem (and this is how it
looks for me) or it''s just some problem with configuration of my
machine. Does anyone else noticed it? Or could someone check? I
appreciate any help.

Regards,
Dawid O.

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Problem was caused by shared info page in
xc_domain_dumpcore_via_callback() in libxenctrl.so.4.0.0. I''m not sure
whether HVM guest should have shared info page but in this case after
restoring domain, shared_info_page was mapped to nonexistent memory and
this was failing while trying to do dump core.

tools/libxc/xc_core.c:498 (Xen 4.1.2)

    if ( xc_domain_getinfo(xch, domid, 1, &info) != 1 ) {...}
    /* Map the shared info frame */
    live_shinfo = xc_map_foreign_range(xch, domid, PAGE_SIZE,
                                       PROT_READ, info.shared_info_frame);

After creating hvm domain from a scratch (`xm create winxp`)
shared_info_frame was set to something looking like a proper frame
number. But after restoring domain (`xm restore ./winxp.save`)
shared_info_frame was set to 0xFFFFFFFFFFFFFFFF.

And then it was failing at tools/libxc/xc_core.c:785
sts = dump_rtn(xch, args, (char*)live_shinfo, PAGE_SIZE);

Because I''m not quite acquainted with Xen source code and
don''t have
much time right now, I haven''t searched deeper (just commented out this
code and recompiled libxenctrl.so).

Regards,
Dawid

On 04.11.2011 01:02, Dawid wrote:
> Hello, I have problem with dumping core of hvm domain. Problem occurs
> only after previously restoring machine from a save file. There is no
> problem with dumping core after creating domain from a scratch and then
> trying to dump. Also there is no such problem with paravirtualized domains.
>
> Error message I got (tried using both xm and xl):
>
> xc: error: Failed to write buffer (14 = Bad address): Internal error
> libxl: error: libxl.c:479:libxl_domain_core_dump core dumping domain 14
> to ./dump.2: Bad address
> core dump failed (rc=-3)
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