On Thu, Oct 24, 2024 at 12:56:25PM -0400, Peter Xu wrote:
> X86 IOMMUs cannot be created more than one on a system yet. Make it a
> singleton so it guards the system from accidentally create yet another
> IOMMU object when one already presents.
>
> Now if someone tries to create more than one, e.g., via:
>
> ./qemu -M q35 -device intel-iommu -device intel-iommu
>
> The error will change from:
>
> qemu-system-x86_64: -device intel-iommu: QEMU does not support multiple
> vIOMMUs for x86 yet.
>
> To:
>
> qemu-system-x86_64: -device intel-iommu: Class 'intel-iommu' only supports
> one instance
>
> Unfortunately, yet we can't remove the singleton check in the machine
> hook (pc_machine_device_pre_plug_cb), because there can also be
> virtio-iommu involved, which doesn't share a common parent class yet.
Presumably the 'class' reported is the one that the user requested,
but this would imply if we were to do
qemu-system-x86_64 -device intel-iommu -device virtio-iommu
Then QEMU would report
"Class 'virtio-iommu' only supports one instance"
at which point the user is wondering, huh, I only requested one virtio-iommu
instance ?
IOW, the current error message would be better as it is not referring to a
specific subclass, but rather to the more general fact that only a single
IOMMU is permitted, no matter what it's impl is.
>
> But with this, it should be closer to reach that goal to check singleton by
> QOM one day.
>
> Signed-off-by: Peter Xu <pet...@redhat.com>
> ---
> hw/i386/x86-iommu.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/hw/i386/x86-iommu.c b/hw/i386/x86-iommu.c
> index 60af896225..4bfeb08705 100644
> --- a/hw/i386/x86-iommu.c
> +++ b/hw/i386/x86-iommu.c
> @@ -26,6 +26,7 @@
> #include "qemu/error-report.h"
> #include "trace.h"
> #include "sysemu/kvm.h"
> +#include "qom/object_interfaces.h"
>
> void x86_iommu_iec_register_notifier(X86IOMMUState *iommu,
> iec_notify_fn fn, void *data)
> @@ -133,10 +134,19 @@ static Property x86_iommu_properties[] = {
> DEFINE_PROP_END_OF_LIST(),
> };
>
> +static Object *x86_iommu_get_instance(Error **errp)
> +{
> + return OBJECT(x86_iommu_get_default());
> +}
> +
> static void x86_iommu_class_init(ObjectClass *klass, void *data)
> {
> DeviceClass *dc = DEVICE_CLASS(klass);
> + SingletonClass *singleton = SINGLETON_CLASS(klass);
> +
> dc->realize = x86_iommu_realize;
> + singleton->get_instance = x86_iommu_get_instance;
> +
> device_class_set_props(dc, x86_iommu_properties);
> }
>
> @@ -152,6 +162,10 @@ static const TypeInfo x86_iommu_info = {
> .class_init = x86_iommu_class_init,
> .class_size = sizeof(X86IOMMUClass),
> .abstract = true,
> + .interfaces = (InterfaceInfo[]) {
> + { TYPE_SINGLETON },
> + { }
> + }
> };
>
> static void x86_iommu_register_types(void)
> --
> 2.45.0
>
With regards,
Daniel
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