Re: BUG at mmu.c:615 from localhost migration using ept+hugetlbfs

[Marcelo Tosatti <mtosatti@redhat.com>]

On Wed, Jun 10, 2009 at 11:08:14AM +0300, Avi Kivity wrote:
> Avi Kivity wrote:
>>
>> Not really.  One thing, migration should transition the shadow  
>> pagetables from large pages to small ones, maybe that bit is broken.
>>
>> Maybe we're looking at a largepage spte and interpreting it as a  
>> normal L2 spte, and interpreting a guest page as the L1 spt.
>
> I tried to find where we drop the mmu (or at least large sptes for the  
> slot) when we enable dirty logging, and failed.  Maybe  
> remove_write_access() is sufficient.

I believe you have to break down large pages into 4k pages for migration
to work reliably. Was tempted to copy&paste the hugetlbfs file ram alloc
code into user/main.c to use with user/vm.c (which then can also be used
to test TLB flushes on 2M->4k transition which are lacking).

Regarding the bogus spte, could not reproduce yesterday with kvm.git,
but in the worst case the audit code will catch it.