Re: [Xen-devel] bug disabling guest interface

["Jacek Milewicz" <jacekowski@xxxxxxxxxxxxxx>]

> I'm interested in knowing more information. Have you always been using
> MAX_SKB_FRAGS > default_value (16 or 17) for you DomUs?

18 used to be default value on older kernels (anything older than 
https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/include/linux/skbuff.h?id=9d4dde5215779f4099730194ad30624fdba3d8b2
 - 
2011-12-23 21:51:18)

> If it is this case, you're likely to be hitting this error path all the 
> time. It is just
> that XSA-39 chooses to shutdown vif if there is something wrong. So my
> further questions is, do you notice any performance problem in the case 
> that
> netback silently drops your packets?

Basically what happened in our case is VMs were migrated to new host with 
new kernel, before that dom0 used to run kernel with MAX_SKB_FRAGS==18 so it 
was same for both dom0 and domU.
New host has kernel with XSA-39 fixes and smaller MAX_SKB_FRAGS (17), and 
that's when we encountered that bug, we've never tried kernel with smaller 
MAX_SKB_FRAGS but without XSA_39 fix.




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