Re: Migration for SPP(Sub-Page Protection) bitmaps

[Yang Weijiang <weijiang.yang@intel.com>]

On Sat, Apr 27, 2019 at 03:37:39AM -0400, Paolo Bonzini wrote:
> 
> > > The destination userspace should simply call KVM_SUBPAGES_SET_ACCESS,
> > > and KVM will process it just like it would on the source.  In other
> > > words, it shouldn't matter if the ioctl is done as part of migration or
> > > the first time a VM is setup.  And in both cases, lazy setup should be
> > > fine.
> > 
> > The problem is in current patch (as in link), it assumes
> > the target pages are there in EPT, but in migration case, these pages
> > are not setup in ETP, so KVM_SUBPAGES_SET_ACCESS during migration or
> > destination bootup will fail, should I modify the patch to setup the
> > ETP in lazy mode?
> 
> Yes, definitely.  Remember that EPT page tables come and go (pages could
> be swapped out, or moved from one host physical address to another; there
> is also a shrinker that will release EPT page tables if memory is low),
> so SPP support should be ready for that.  Migration is just a special case.
> 
> Paolo
 OK, got it, thanks a lot for the reply!