Re: [Qemu-devel] [PATCH v2 14/23] hyperv: qom-ify SynIC

[Roman Kagan]

On Fri, Jul 07, 2017 at 02:22:20PM +0200, Igor Mammedov wrote:
> On Thu, 29 Jun 2017 20:51:01 +0300
> Roman Kagan <address@hidden> wrote:
> 
> > On Thu, Jun 29, 2017 at 05:05:46PM +0200, Igor Mammedov wrote:
> > > On Wed, 21 Jun 2017 19:24:15 +0300
> > > Roman Kagan <address@hidden> wrote:  
> [...]
> > 
> > > > +    if (cpu->hyperv_synic) {
> > > > +        if (kvm_vcpu_enable_cap(CPU(cpu), KVM_CAP_HYPERV_SYNIC, 0)) {
> > > > +            fprintf(stderr, "failed to enable Hyper-V SynIC\n");
> > > > +            return -ENOSYS;
> > > > +        }
> > > > +
> > > > +        hyperv_synic_add(cpu);  
> > > is synic KVM specific or may it work with TCG accel?  
> > 
> > No, it's exclusively KVM.  Actually most of it sits in the kernel.
> > 
> > > in either case, looks like hyperv_synic_add() should be called from
> > > x86_cpu_realizefn(), the same like we do with APIC creating it
> > > depending feature being enabled.  
> > 
> > I'm not sure I understand the reason, in view of it being exclusively
> > KVM.
> couldn't synic be emulated (if missing QEMU part is written) in TCG mode
> or it relies on specific KVM features?

At the moment it depends on KVM and, in particular, relies on lapic
being in KVM.  I guess with certain effort it can be done in TCG too,
but we didn't even consider this so far, and have no plans for it.

Roman.