Re: [Qemu-devel] Async savevm using userfaultfd(2)

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Stefan Hajnoczi (stefanha@gmail.com) wrote:
> On Wed, Oct 12, 2016 at 4:04 PM, Stefan Hajnoczi <stefanha@gmail.com> wrote:
> > Perhaps this approach can be prototyped with mprotect and a SIGSEGV
> > handler if anyone wants to get async savevm going.  I don't know if
> > there are any disadvantages to mprotecting guest RAM that the kvm kernel
> > module is using.  Hopefully in-kernel devices and vhost will continue to
> > work.
> 
> I woke up this morning with a strong feeling that a SIGSEGV handler
> won't work with vhost.

YKYBHTLW you wake up with strong feelings about SIGSEGV handlers.

>  The problem is that the QEMU process' SIGSEGV
> handler won't be called when the vhost kernel thread faults.  Now I'm
> wondering whether userfaultfd will work together with vhost.

I think it should, or at least I think all other kernel things end up being
caught by userfaultfd during postcopy.

Dave

> Stefan
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK