[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Xen 4.0.0x allows for data corruption in Dom0
On 03/09/2010 12:12 AM, Jeremy Fitzhardinge wrote: > I think its most likely to be a dom0 bug, specifically a bug in one of > the backend drivers. The common failure mode which causes symtoms like > this is when a granted page (=a domU page mapped into dom0) is released > back into dom0's heap and reused as general memory while still being > under the control of the domU. > > However, given that the domU hasn't got any devices assigned to it aside > from the console, none of the backend should be coming into play. It > might be a more general problem with the privcmd interface. > > Alternatively, I suppose, the domain builder could end up using some of > dom0 pages to construct the domU without properly freeing them, which > would suggest a bug in the balloon driver. > > I can't think of a Xen failure-mode which would cause these symptoms > without also being massively obvious in other cases. (But "I can't > think of..." is where all the best bugs hide.) > But the corruptions always happen in 32-bytes chunks, which might suggest it's not a page-related problem (e.g. wrongly re-used page), as in that case we would be observing (at least sometimes) much bigger chunks of corrupted data, I think. The reason why I still believe it's a hypervisor related thing, it that I'm currently using the very *same* Dom0 kernel (very recent xen/stable-2.6.31) with Xen 3.4.2 and the system is damn stable. And I really mean extensive use with 5-7 VMs running all the time doing various things from Web browsing to kernel building. If I was to make an educated guess I would say it's something related to some interrupt handling, i.e. Xen mishandling it, e.g. the handler is writing out-of-buffer somewhere and it just happens to land in the Dom0 fs buffer used by e.g. dd operation. joanna. Attachment:
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