Re: [Qemu-arm] [PATCH v2 3/3] arm: implement query-gic-capability

[Peter Xu <peterx@redhat.com>]

On Thu, Mar 03, 2016 at 01:19:47PM +0100, Andrea Bolognani wrote:
> On Thu, 2016-03-03 at 16:21 +0800, Peter Xu wrote:
> > For emulated ARM VM, only gicv2 is supported. We need to add gicv3
> in
> > when emulated gicv3 ready. For KVM accelerated ARM VM, we detect the
> > capability bits using ioctls.
> > 
> > if we want to
> know GIC kernel capabilities, we need to make sure we have
> > enabled KVM when querying (like, with "-enable-kvm").
> > 
> >
> Signed-off-by: Peter Xu <peterx@redhat.com>
> > ---
> >  target-arm/machine.c | 48
> +++++++++++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 47 insertions(+), 1 deletion(-)
> 
> Sorry for not catching this earlier, but I'm afraid this is not
> going to work -- libvirt doesn't pass either -enable-kvm or the
> machine option accel=kvm when probing for capabilities, which
> means that, with the current implementation, it will only get
> information about emulated GIC.
> 
> Is there a way to make probing work without requiring KVM to
> be enabled?

Ah.. If so, this is a good point...

I can do this, but I just feel it a bit hacky if I do ioctl()s
directly in one QMP command handle:

qmp_query_gic_capability()
{
    kvm = open("/dev/kvm");
    vm = ioctl(KVM_CREATE_VM);

    ...test create devices using KVM_CREATE_DEVICE ioctls...

    close(vm);
    close(kvm);
}

Rather than leveraging current KVMState stuffs (of course, I can
make things a little bit prettier than above...).

Another way to do is to generalize kvm_init() maybe? That's some
work too.

Andrea, do you know how much effort we need to add this support for
libvirt, say, we can specify "accel=" or "-enable-kvm" as extra
parameter when probing?

Or, does anyone on the list has suggestion on how to better do this?

Thanks.
Peter