On Tue, Aug 13, 2019 at 02:09:51PM +0200, Paolo Bonzini wrote:
> On 13/08/19 13:57, Adalbert Lazăr wrote:
> >> The refcounting approach seems a bit backwards, and AFAICT is driven by
> >> implementing unhook via a message, which also seems backwards. I assume
> >> hook and unhook are relatively rare events and not performance critical,
> >> so make those the restricted/slow flows, e.g. force userspace to quiesce
> >> the VM by making unhook() mutually exclusive with every vcpu ioctl() and
> >> maybe anything that takes kvm->lock.
> >>
> >> Then kvmi_ioctl_unhook() can use thread_stop() and kvmi_recv() just needs
> >> to check kthread_should_stop().
> >>
> >> That way kvmi doesn't need to be refcounted since it's guaranteed to be
> >> alive if the pointer is non-null. Eliminating the refcounting will clean
> >> up a lot of the code by eliminating calls to kvmi_{get,put}(), e.g.
> >> wrappers like kvmi_breakpoint_event() just check vcpu->kvmi, or maybe
> >> even get dropped altogether.
> >
> > The unhook event has been added to cover the following case: while the
> > introspection tool runs in another VM, both VMs, the virtual appliance
> > and the introspected VM, could be paused by the user. We needed a way
> > to signal this to the introspection tool and give it time to unhook
> > (the introspected VM has to run and execute the introspection commands
> > during this phase). The receiving threads quits when the socket is closed
> > (by QEMU or by the introspection tool).
Why does closing the socket require destroying the kvmi object? E.g. can
it be marked as defunct or whatever and only fully removed on a synchronous
unhook from userspace? Re-hooking could either require said unhook, or
maybe reuse the existing kvmi object with a new socket.
> > It's a bit unclear how, but we'll try to get ride of the refcount object,
> > which will remove a lot of code, indeed.
>
> You can keep it for now. It may become clearer how to fix it after the
> event loop is cleaned up.
By event loop, do you mean the per-vCPU jobs list?
