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Re: Dom0 ballooning: crash on guest start

On 29.04.2011 15:02, Christoph Egger wrote:
>>> balloon0: inflate 512 => inflated by 512
>>> uvm_fault(0xffffffff80c6b220, 0xffffffff81400000, 1) -> e
>>> fatal page fault in supervisor mode
>>> trap type 6 code 0 rip ffffffff8054593d cs e030 rflags 10216 cr2
>> Okay, happens when balloon(4) has already been inflated by a good share.
>> Out of interest, having XENDEBUG_SYNC enabled in
>> arch/xen/x86/x86_xpmap.c does not change anything to the result?
> No effect.

I can reliably trigger the issue. It's due to the domain doing P2M page
frame number translations via the xpmap_phys_to_machine_mapping array
for specific PFNs in the 3GiB range.

For amd64, index are from 0xbd000 to 0xbd200 (one page, mapping physical
pages 3024 => 3026MiB).

Now, why there is this 2MiB hole right there in the pseudo-physical
map... is the next question. They have no direct connection to machine
(real) addresses, and there's nothing like this appearing in the
dom0/hypervisor domain_build code (xen/arch/x86/domain_build.c).

Jean-Yves Migeon

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