Re: [Xen-devel] Very strange behavior between balloon driver and network driver (Arndale)

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2013-05-28 at 12:14 +0000, Jaeyong Yoo wrote:
> Hello,
> I'm testing xen in Arndale board and I found very strange behavior:
> 
> When I'm creating/destroying domUs consecutively, suddenly network
> driver does not work.
> I tried both on-board and USB-dongle network devices but they show the
> similar behavior.

I expect that the ballooning up and down is counteracting the affect of
the 1:1 workaround which is required on the Arndale due to lack of an
IOMMU driver.

As a workaround I would recommend using dom0_mem=<something> and
disabling autoballooning.

Of course if, as a Sumsung developer, you are able to gain access to the
documentation necessary to write an IOMMU driver for the Arndale
platform that would be great!

Ian.

> Only difference is that when I'm using on-board, it gives the
> following error message:
> 
>  
> 
> [ 709.900000] asix 1-3.2.4:1.0 eth0: asix_rx_fixup() Bad Header Length
> 0x85555, offset 4 
> [ 709.910000] asix 1-3.2.4:1.0 eth0: asix_rx_fixup() Bad Header Length
> 0x0, offset 4 
> [ 709.920000] asix 1-3.2.4:1.0 eth0: asix_rx_fixup() Bad Header Length
> 0x0, offset 4 
> [ 709.930000] asix 1-3.2.4:1.0 eth0: asix_rx_fixup() Bad Header Length
> 0x105555, offset 4 
> 
> while USB-dongle network device does not show any message.
> 
>  
> 
> I investigated this problem and found out that when I comment out the
> following line 
> in file drivers/xen/balloon.c at function free_xenballooned_pages as
> follows, 
> 
>         //if (current_credit())
>         //      schedule_delayed_work(&balloon_worker, 0);
> , the problem disappears.
> balloon_worker is doing increase_reservation and decrease_reservation
> that use XENMEM 
> 
> hypercalls. I think while mapping and unmapping domain pages with the
> above hypercalls, 
> 
> somehow the network driver memory is corrupted.
> 
>  
> 
> Currently, most suspcious function is create_p2m_entries in xen
> (xen/arch/arm/p2m.c)
> When we call this function with INSERT op, it maps the corresponding
> pte (page table entry)
> 
> to the given mfn without checking whether the pte is already take by
> someone. 
> I actually observed that pte's base address is overwritten to some
> other value and I'm not sure 
> 
> this behavior is OK. If it is not OK, I think it can corrupt others
> memory (for instance, inocent 
> 
> network driver). 
> 
>  
> 
> Do you have any ideas or experience similar bug (the network error)?
> 
>  
> 
> Best,
> 
> Jaeyong
> 
>  
> 
> 
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> http://lists.xen.org/xen-devel



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