Re: [RFC PATCH v1 3/4] KVM: arm64: GICv4.1: Restore VLPI's pending state to physical side

[Marc Zyngier]

On 2020-12-01 11:40, Shenming Lu wrote:
> On 2020/12/1 18:55, Marc Zyngier wrote:
> > On 2020-11-30 07:23, Shenming Lu wrote:
> >
> > Hi Shenming,
> >
> > > We are pondering over this problem these days, but still don't get a
> > > good solution...
> > > Could you give us some advice on this?
> > >
> > > Or could we move the restoring of the pending states (include the 
> > > sync
> > > from guest RAM and the transfer to HW) to the GIC VM state change 
> > > handler,
> > > which is completely corresponding to save_pending_tables (more 
> > > symmetric?)
> > > and don't expose GICv4...
> >
> > What is "the GIC VM state change handler"? Is that a QEMU thing?
>
> Yeah, it is a a QEMU thing...
>
> > We don't really have that concept in KVM, so I'd appreciate if you 
> > could
> > be a bit more explicit on this.
>
> My thought is to add a new interface (to QEMU) for the restoring of
> the pending states, which is completely corresponding to
> KVM_DEV_ARM_VGIC_SAVE_PENDING_TABLES...
> And it is called from the GIC VM state change handler in QEMU, which
> is happening after the restoring (call kvm_vgic_v4_set_forwarding())
> but before the starting (running) of the VFIO device.

Right, that makes sense. I still wonder how much the GIC save/restore
stuff differs from other architectures that implement similar features,
such as x86 with VT-D.

It is obviously too late to change the userspace interface, but I wonder
whether we missed something at the time.

Thanks,

        M.
--
Jazz is not dead. It just smells funny...