Re: [PATCH 2/2] kvm: clear dirty bitmaps from all overlapping memslots

[Peter Xu <peterx@redhat.com>]

On Fri, Sep 20, 2019 at 12:21:22PM +0200, Paolo Bonzini wrote:
> Since the KVM dirty page reporting works on guest physical addresses,
> we need to clear all of the aliases when a page is migrated, or there
> is a risk of losing writes to the aliases that were not cleared.

The patch content looks perfect to me, though I just want to make sure
I understand the issue behind, and the commit message...

IMHO we've got two issues to cover for log_clear():

  (1) memory region aliasing, hence multiple GPAs can point to the same
      HVA/HPA so we need to clear the memslot dirty bits on all the
      mapped GPAs, and,

  (2) large log_clear() request which can cover more than one valid
      kvm memslots.  Note that in this case, the mem slots can really
      be having different HVAs so imho it should be a different issue
      comparing to (1)

The commit message says it's solving problem (1).  However for what I
understand, we are actually doing well on issue (1) because in
memory_region_clear_dirty_bitmap() we iterate over all the flat views
so that we should have caught all the aliasing memory regions if there
are any.  However this patch should perfectly fix problem (2).  Am I
right?

Thanks,

-- 
Peter Xu