On Fri, Mar 28, 2014 at 10:39:25AM -0700, Mario Smarduch wrote:
> Hello
> 
> I've been working on live migration for ARM-KVM, and noticed
> problem completing migration with huge 2nd stage tables.
>  
> 
> Aafter write protecting the VM, for write fault 512 page bits
> are set in dirty_bitmap[] to take into account future writes to 
> huge page.The pmd is write protected again when QEMU  reads the 
> dirty log, and the cycle repeats. With this not even a idle 
> 32MB VM  completes live migration.
> 
> If QEMU uses THPs, and 2nd stage tables use pte's, then there
> is no problem, live migration is quick. I'm assumung QEMU and Guest 
> huge pages with 2nd stage page table pte's should work fine too.
> 
> I'm wondering how this has been solved (for any architecture)? 
> 
I don't know if there's a generic solution (have you looked at x86/PPC
what they do?), but I don't see any conceptual problem with putting the
VM into use-pte-for-2nd-stage-mappings-I'm-migrating-mode.

-Christoffer
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