On Thu, May 09, 2013 at 05:00:20PM +0800, liu ping fan wrote: > On Thu, May 9, 2013 at 4:30 PM, Stefan Hajnoczi <stefa...@gmail.com> wrote: > > On Thu, May 09, 2013 at 08:40:21AM +0800, Liu Ping Fan wrote: > >> From: Liu Ping Fan <pingf...@linux.vnet.ibm.com> > >> > >> Hosts threads which handle vring should have high MemoryListener priority > >> than kvm. For currently code, take the following scenario: > >> kvm_region_add() run earlier before vhost_region_add(), then in guest, > >> vring's desc[i] can refer to addressX in the new region known by guest. > >> But vhost does not know this new region yet, and the vring handler will > >> fail. > > > > Is there a concrete scenario where this happens? > > > > I can think of situations like the ioeventfd being readable before > > vhost/hostmem is populated. But I don't see how that's related to the > > priority of kvm_region_add(). > > > For kvm, ie, In guest, vring_desc.addr can point to a chunk of data in > the new added memory, and kick vhost. The vhost has not added this new > region, so its local lookup table can not translate this new address, > and vring handler will fail. If vhost priority is higher than kvm, > then, it will know this new address earlier than kvm.
Isn't the real solution to ensure that the memory API is up-to-date before we notify the guest of memory hotplug? I still don't see a kvm vs vhost race. I see a guest vs vhost race which priority doesn't fix. Stefan