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

[Cédric Le Goater]

On 7/30/25 12:55, Duan, Zhenzhong wrote:

-----Original Message-----
From: Cédric Le Goater <c...@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 <nicol...@nvidia.com>
Suggested-by: Yi Liu <yi.l....@intel.com>
Signed-off-by: Zhenzhong Duan <zhenzhong.d...@intel.com>
Reviewed-by: Eric Auger <eric.au...@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.