Re: [PATCH v4 04/20] vfio/iommufd: Force creating nested parent domain

["Cédric Le Goater" <clg@redhat.com>]

On 7/30/25 12:55, Duan, Zhenzhong wrote:
> 
> 
>> -----Original Message-----
>> From: Cédric Le Goater <clg@redhat.com>
>> Subject: Re: [PATCH v4 04/20] vfio/iommufd: Force creating nested parent
>> domain
>>
>> On 7/29/25 11:20, Zhenzhong Duan wrote:
>>> Call pci_device_get_viommu_cap() to get if vIOMMU supports
>> VIOMMU_CAP_HW_NESTED,
>>> if yes, create nested parent domain which could be reused by vIOMMU to
>> create
>>> nested domain.
>>>
>>> It is safe because hw_caps & VIOMMU_CAP_HW_NESTED cannot be set yet
>> because
>>> s->flts is forbidden until we support passthrough device with x-flts=on.
>>>
>>> Suggested-by: Nicolin Chen <nicolinc@nvidia.com>
>>> Suggested-by: Yi Liu <yi.l.liu@intel.com>
>>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
>>> Reviewed-by: Eric Auger <eric.auger@redhat.com>
>>> ---
>>>    hw/vfio/iommufd.c | 14 ++++++++++++++
>>>    1 file changed, 14 insertions(+)
>>>
>>> diff --git a/hw/vfio/iommufd.c b/hw/vfio/iommufd.c
>>> index 48c590b6a9..61a548f13f 100644
>>> --- a/hw/vfio/iommufd.c
>>> +++ b/hw/vfio/iommufd.c
>>> @@ -20,6 +20,7 @@
>>>    #include "trace.h"
>>>    #include "qapi/error.h"
>>>    #include "system/iommufd.h"
>>> +#include "hw/iommu.h"
>>>    #include "hw/qdev-core.h"
>>>    #include "hw/vfio/vfio-cpr.h"
>>>    #include "system/reset.h"
>>> @@ -379,6 +380,19 @@ static bool
>> iommufd_cdev_autodomains_get(VFIODevice *vbasedev,
>>>            flags = IOMMU_HWPT_ALLOC_DIRTY_TRACKING;
>>>        }
>>>
>>> +    /*
>>> +     * If vIOMMU supports stage-1 translation, force to create nested
>> parent
>>> +     * domain which could be reused by vIOMMU to create nested
>> domain.
>>> +     */
>>> +    if (vbasedev->type == VFIO_DEVICE_TYPE_PCI) {
>>> +        VFIOPCIDevice *vdev = container_of(vbasedev, VFIOPCIDevice,
>> vbasedev);
>>> +
>>> +        hw_caps = pci_device_get_viommu_cap(&vdev->pdev);
>>> +        if (hw_caps & VIOMMU_CAP_HW_NESTED) {
>>> +            flags |= IOMMU_HWPT_ALLOC_NEST_PARENT;
>>> +        }
>>> +    }
>>>
>>
>> Could you please add a wrapper for the above ? Something like :
>>
>> static bool vfio_device_viommu_get_nested(VFIODevice *vbasedev)
>> {
>>      if (vbasedev->type == VFIO_DEVICE_TYPE_PCI) {
>>          VFIOPCIDevice *vdev = container_of(vbasedev, VFIOPCIDevice,
>> vbasedev);
>>
>> 	return !!(pci_device_get_viommu_cap(&vdev->pdev) &
>> VIOMMU_CAP_HW_NESTED);
>>      }
>>      return false;
>> }
>>
>> May be this routine belongs to hw/vfio/device.c.
> 
> Done, see https://github.com/yiliu1765/qemu/commit/7ce1af90d5c1f418f23c9e397a16a3914b30f09f
> 
> I also introduced another wrapper vfio_device_to_vfio_pci(), let me know if you think it's unnecessary, I'll fold it.

It's good to have it if you use it everywhere:

hw/vfio/device.c:    if (vbasedev->type != VFIO_DEVICE_TYPE_PCI) {
hw/vfio/container.c:                vbasedev_iter->type != VFIO_DEVICE_TYPE_PCI) {
hw/vfio/container.c:                vbasedev_iter->type != VFIO_DEVICE_TYPE_PCI) {
hw/vfio/listener.c:    if (vbasedev && vbasedev->type == VFIO_DEVICE_TYPE_PCI) {
hw/vfio/listener.c:        if (vbasedev->type != VFIO_DEVICE_TYPE_PCI) {
hw/vfio/iommufd.c:    if (vbasedev->type == VFIO_DEVICE_TYPE_PCI) {
hw/vfio/iommufd.c:        vbasedev_tmp->type != VFIO_DEVICE_TYPE_PCI) {

So, I would address this cleanup separately.

FYI, We also have this helper :

VFIODevice *vfio_get_vfio_device(Object *obj)
{
     if (object_dynamic_cast(obj, TYPE_VFIO_PCI)) {
         return &VFIO_PCI_BASE(obj)->vbasedev;
     } else {
         return NULL;
     }
}


Thanks,

C.