[PATCH v8 05/23] hw/pci: Introduce pci_device_get_viommu_flags()

[Zhenzhong Duan <zhenzhong.duan@intel.com>]

Introduce a new PCIIOMMUOps optional callback, get_viommu_flags() which
allows to retrieve flags exposed by a vIOMMU. The first planned vIOMMU
device flag is VIOMMU_FLAG_WANT_NESTING_PARENT that advertises the
support of HW nested stage translation scheme and wants other sub-system
like VFIO's cooperation to create nesting parent HWPT.

pci_device_get_viommu_flags() is a wrapper that can be called on a PCI
device potentially protected by a vIOMMU.

get_viommu_flags() is designed to return 64bit bitmap of purely vIOMMU
flags which are only determined by user's configuration, no host
capabilities involved. Reasons are:

1. host may has heterogeneous IOMMUs, each with different capabilities
2. this is migration friendly, return value is consistent between source
   and target.

Note that this op will be invoked at the attach_device() stage, at which
point host IOMMU capabilities are not yet forwarded to the vIOMMU through
the set_iommu_device() callback that will be after the attach_device().

See below sequence:

  vfio_device_attach():
      iommufd_cdev_attach():
          pci_device_get_viommu_flags() for HW nesting cap
          create a nesting parent HWPT
          attach device to the HWPT
          vfio_device_hiod_create_and_realize() creating hiod
  ...
  pci_device_set_iommu_device(hiod)

Suggested-by: Yi Liu <yi.l.liu@intel.com>
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Yi Liu <yi.l.liu@intel.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
---
 MAINTAINERS          |  1 +
 include/hw/iommu.h   | 25 +++++++++++++++++++++++++
 include/hw/pci/pci.h | 22 ++++++++++++++++++++++
 hw/pci/pci.c         | 11 +++++++++++
 4 files changed, 59 insertions(+)
 create mode 100644 include/hw/iommu.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 9cb181e1da..f4a30c126b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2344,6 +2344,7 @@ F: include/system/iommufd.h
 F: backends/host_iommu_device.c
 F: include/system/host_iommu_device.h
 F: include/qemu/chardev_open.h
+F: include/hw/iommu.h
 F: util/chardev_open.c
 F: docs/devel/vfio-iommufd.rst
 
diff --git a/include/hw/iommu.h b/include/hw/iommu.h
new file mode 100644
index 0000000000..9b8bb94fc2
--- /dev/null
+++ b/include/hw/iommu.h
@@ -0,0 +1,25 @@
+/*
+ * General vIOMMU flags
+ *
+ * Copyright (C) 2025 Intel Corporation.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#ifndef HW_IOMMU_H
+#define HW_IOMMU_H
+
+#include "qemu/bitops.h"
+
+/*
+ * Theoretical vIOMMU flags. Only determined by the vIOMMU device properties and
+ * independent on the actual host IOMMU capabilities they may depend on. Each
+ * flag can be an expectation or request to other sub-system or just a pure
+ * vIOMMU capability. vIOMMU can choose which flags to expose.
+ */
+enum viommu_flags {
+    /* vIOMMU needs nesting parent HWPT to create nested HWPT */
+    VIOMMU_FLAG_WANT_NESTING_PARENT = BIT_ULL(0),
+};
+
+#endif /* HW_IOMMU_H */
diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
index bde9dca8e2..a3ca54859c 100644
--- a/include/hw/pci/pci.h
+++ b/include/hw/pci/pci.h
@@ -462,6 +462,18 @@ typedef struct PCIIOMMUOps {
      * @devfn: device and function number of the PCI device.
      */
     void (*unset_iommu_device)(PCIBus *bus, void *opaque, int devfn);
+    /**
+     * @get_viommu_flags: get vIOMMU flags
+     *
+     * Optional callback, if not implemented, then vIOMMU doesn't support
+     * exposing flags to other sub-system, e.g., VFIO.
+     *
+     * @opaque: the data passed to pci_setup_iommu().
+     *
+     * Returns: bitmap with each bit representing a vIOMMU flag defined in
+     * enum viommu_flags.
+     */
+    uint64_t (*get_viommu_flags)(void *opaque);
     /**
      * @get_iotlb_info: get properties required to initialize a device IOTLB.
      *
@@ -644,6 +656,16 @@ bool pci_device_set_iommu_device(PCIDevice *dev, HostIOMMUDevice *hiod,
                                  Error **errp);
 void pci_device_unset_iommu_device(PCIDevice *dev);
 
+/**
+ * pci_device_get_viommu_flags: get vIOMMU flags.
+ *
+ * Returns: bitmap with each bit representing a vIOMMU flag defined in
+ * enum viommu_flags. Or 0 if vIOMMU doesn't report any.
+ *
+ * @dev: PCI device pointer.
+ */
+uint64_t pci_device_get_viommu_flags(PCIDevice *dev);
+
 /**
  * pci_iommu_get_iotlb_info: get properties required to initialize a
  * device IOTLB.
diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index 3eb57b96ea..8b62044a8e 100644
--- a/hw/pci/pci.c
+++ b/hw/pci/pci.c
@@ -3021,6 +3021,17 @@ void pci_device_unset_iommu_device(PCIDevice *dev)
     }
 }
 
+uint64_t pci_device_get_viommu_flags(PCIDevice *dev)
+{
+    PCIBus *iommu_bus;
+
+    pci_device_get_iommu_bus_devfn(dev, &iommu_bus, NULL, NULL);
+    if (iommu_bus && iommu_bus->iommu_ops->get_viommu_flags) {
+        return iommu_bus->iommu_ops->get_viommu_flags(iommu_bus->iommu_opaque);
+    }
+    return 0;
+}
+
 int pci_pri_request_page(PCIDevice *dev, uint32_t pasid, bool priv_req,
                          bool exec_req, hwaddr addr, bool lpig,
                          uint16_t prgi, bool is_read, bool is_write)
-- 
2.47.1