Bug#676360: xen: oops at atomic64_read_cx8+0x4

[Sergio Gelato <Sergio.Gelato@astro.su.se>]

* Andrea Arcangeli [2012-06-07 12:33:55 +0200]:
> I guess if Xen can't be updated to handle an atomic64_read on a pmd in
> the guest, 

I'm not sure if it makes a difference, but just in case: I observed the
problem in a dom0.

>            we can add a pmd_read paravirt op? Or if we don't want to
> break the paravirt interface a loop like gup_fast with irq disabled
> should also work but looping + local_irq_disable()/enable() sounded
> worse and more complex than a atomic64_read (gup fast already disables
> irqs because it doesn't hold the mmap_sem so it's a different cost
> looping there). AFIK Xen disables THP during boot, so a check on THP
> being enabled and falling back in the THP=n version of
> pmd_read_atomic, would also be safe, but it's not so nice to do it
> with a runtime check.
> 
> Thanks,
> Andrea