In preparation to using the dirty tracking UAPI, probe whether the IOMMU
supports dirty tracking. This is done via the data stored in
hiod::caps::hw_caps initialized from GET_HW_INFO.

Qemu doesn't know if VF dirty tracking is supported when allocating
hardware pagetable in iommufd_cdev_autodomains_get(). This is because
VFIODevice migration state hasn't been initialized *yet* hence it can't pick
between VF dirty tracking vs IOMMU dirty tracking. So, if IOMMU supports
dirty tracking it always creates HWPTs with IOMMU_HWPT_ALLOC_DIRTY_TRACKING
even if later on VFIOMigration decides to use VF dirty tracking instead.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
---
 include/hw/vfio/vfio-common.h |  1 +
 hw/vfio/iommufd.c             | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
index 4e44b26d3c45..7e530c7869dc 100644
--- a/include/hw/vfio/vfio-common.h
+++ b/include/hw/vfio/vfio-common.h
@@ -97,6 +97,7 @@ typedef struct IOMMUFDBackend IOMMUFDBackend;
 
 typedef struct VFIOIOASHwpt {
     uint32_t hwpt_id;
+    uint32_t hwpt_flags;
     QLIST_HEAD(, VFIODevice) device_list;
     QLIST_ENTRY(VFIOIOASHwpt) next;
 } VFIOIOASHwpt;
diff --git a/hw/vfio/iommufd.c b/hw/vfio/iommufd.c
index bb44d948c735..2e5c207bbca0 100644
--- a/hw/vfio/iommufd.c
+++ b/hw/vfio/iommufd.c
@@ -110,6 +110,11 @@ static void iommufd_cdev_unbind_and_disconnect(VFIODevice *vbasedev)
     iommufd_backend_disconnect(vbasedev->iommufd);
 }
 
+static bool iommufd_hwpt_dirty_tracking(VFIOIOASHwpt *hwpt)
+{
+    return hwpt && hwpt->hwpt_flags & IOMMU_HWPT_ALLOC_DIRTY_TRACKING;
+}
+
 static int iommufd_cdev_getfd(const char *sysfs_path, Error **errp)
 {
     ERRP_GUARD();
@@ -246,6 +251,17 @@ static bool iommufd_cdev_autodomains_get(VFIODevice *vbasedev,
         }
     }
 
+    /*
+     * This is quite early and VFIO Migration state isn't yet fully
+     * initialized, thus rely only on IOMMU hardware capabilities as to
+     * whether IOMMU dirty tracking is going to be requested. Later
+     * vfio_migration_realize() may decide to use VF dirty tracking
+     * instead.
+     */
+    if (vbasedev->hiod->caps.hw_caps & IOMMU_HW_CAP_DIRTY_TRACKING) {
+        flags = IOMMU_HWPT_ALLOC_DIRTY_TRACKING;
+    }
+
     if (!iommufd_backend_alloc_hwpt(iommufd, vbasedev->devid,
                                     container->ioas_id, flags,
                                     IOMMU_HWPT_DATA_NONE, 0, NULL,
@@ -255,6 +271,7 @@ static bool iommufd_cdev_autodomains_get(VFIODevice *vbasedev,
 
     hwpt = g_malloc0(sizeof(*hwpt));
     hwpt->hwpt_id = hwpt_id;
+    hwpt->hwpt_flags = flags;
     QLIST_INIT(&hwpt->device_list);
 
     ret = iommufd_cdev_attach_ioas_hwpt(vbasedev, hwpt->hwpt_id, errp);
@@ -267,6 +284,8 @@ static bool iommufd_cdev_autodomains_get(VFIODevice *vbasedev,
     vbasedev->hwpt = hwpt;
     QLIST_INSERT_HEAD(&hwpt->device_list, vbasedev, hwpt_next);
     QLIST_INSERT_HEAD(&container->hwpt_list, hwpt, next);
+    container->bcontainer.dirty_pages_supported |=
+                              iommufd_hwpt_dirty_tracking(hwpt);
     return true;
 }
 
-- 
2.17.2