Re: [Qemu-devel] [RFC 3/4] hw/intc/arm_gicv3_its: Implement state save/restore

[Juan Quintela <quintela@redhat.com>]

Eric Auger <eric.auger@redhat.com> wrote:
> We need to handle both registers and ITS tables. While
> register handling is standard, ITS table handling is more
> challenging since the kernel API is devised so that the
> tables are flushed into guest RAM and not in vmstate buffers.
>
> Flushing the ITS tables on device pre_save() is too late
> since the guest RAM had already been saved at this point.
>
> Table flushing needs to happen when we are sure the vcpus
> are stopped and before the last dirty page saving. The
> right point is RUN_STATE_FINISH_MIGRATE but sometimes the
> VM gets stopped before migration launch so let's simply
> flush the tables each time the VM gets stopped.
>
> For regular ITS registers we just can use vmstate pre_save
> and post_load callbacks.
>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>

Hi


> + * vm_change_state_handler - VM change state callback aiming at flushing
> + * ITS tables into guest RAM
> + *
> + * The tables get flushed to guest RAM whenever the VM gets stopped.
> + */
> +static void vm_change_state_handler(void *opaque, int running,
> +                                    RunState state)
> +{
> +    GICv3ITSState *s = (GICv3ITSState *)opaque;

Cast is unneeded.

> +
> +    if (running) {
> +        return;
> +    }
> +    kvm_device_access(s->dev_fd, KVM_DEV_ARM_VGIC_GRP_ITS_TABLES,
> +                      0, NULL, false);

As you are adding it to do everytime that we stop the guest, how
expensive/slow is that?

Thanks, Juan.