From: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>

In order to enable device assignment with IOMMU protection and guest DMA
address translation, IOMMU MAP notifier support is necessary to allow users
like VFIO to synchronize the shadow page tables i.e. to receive
notifications when the guest updates its I/O page tables and replay the
mappings onto host I/O page tables.

Provide a new dma-remap property to govern the ability to register for MAP
notifications, effectively providing global control over the DMA address
translation functionality that was implemented in previous changes.

Note that DMA remapping support also requires the vIOMMU is configured with
the NpCache capability, so a guest driver issues IOMMU invalidations for
both map() and unmap() operations. This capability is already set by default
and written to the configuration in amdvi_pci_realize() as part of
AMDVI_CAPAB_FEATURES.

Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <20250919213515.917111-18-alejandro.j.jimenez@oracle.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/i386/amd_iommu.h |  3 +++
 hw/i386/amd_iommu.c | 24 +++++++++++++++++-------
 2 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/hw/i386/amd_iommu.h b/hw/i386/amd_iommu.h
index b51aa74368..e1354686b6 100644
--- a/hw/i386/amd_iommu.h
+++ b/hw/i386/amd_iommu.h
@@ -418,6 +418,9 @@ struct AMDVIState {
     /* Interrupt remapping */
     bool ga_enabled;
     bool xtsup;
+
+    /* DMA address translation */
+    bool dma_remap;
 };
 
 uint64_t amdvi_extended_feature_register(AMDVIState *s);
diff --git a/hw/i386/amd_iommu.c b/hw/i386/amd_iommu.c
index e9ce7b46e8..ce5d4c3662 100644
--- a/hw/i386/amd_iommu.c
+++ b/hw/i386/amd_iommu.c
@@ -990,7 +990,9 @@ static void amdvi_iommu_address_space_sync_all(AMDVIState *s)
  */
 static void amdvi_switch_address_space(AMDVIAddressSpace *amdvi_as)
 {
-    if (amdvi_as->addr_translation) {
+    AMDVIState *s = amdvi_as->iommu_state;
+
+    if (s->dma_remap && amdvi_as->addr_translation) {
         /* Enabling DMA region */
         memory_region_set_enabled(&amdvi_as->iommu_nodma, false);
         memory_region_set_enabled(MEMORY_REGION(&amdvi_as->iommu), true);
@@ -2193,12 +2195,19 @@ static int amdvi_iommu_notify_flag_changed(IOMMUMemoryRegion *iommu,
     AMDVIAddressSpace *as = container_of(iommu, AMDVIAddressSpace, iommu);
     AMDVIState *s = as->iommu_state;
 
-    if (new & IOMMU_NOTIFIER_MAP) {
-        error_setg(errp,
-                   "device %02x.%02x.%x requires iommu notifier which is not "
-                   "currently supported", as->bus_num, PCI_SLOT(as->devfn),
-                   PCI_FUNC(as->devfn));
-        return -EINVAL;
+    /*
+     * Accurate synchronization of the vIOMMU page tables required to support
+     * MAP notifiers is provided by the dma-remap feature. In addition, this
+     * also requires that the vIOMMU presents the NpCache capability, so a guest
+     * driver issues invalidations for both map() and unmap() operations. The
+     * capability is already set by default as part of AMDVI_CAPAB_FEATURES and
+     * written to the configuration in amdvi_pci_realize().
+     */
+    if (!s->dma_remap && (new & IOMMU_NOTIFIER_MAP)) {
+        error_setg_errno(errp, ENOTSUP,
+            "device %02x.%02x.%x requires dma-remap=1",
+            as->bus_num, PCI_SLOT(as->devfn), PCI_FUNC(as->devfn));
+        return -ENOTSUP;
     }
 
     /*
@@ -2423,6 +2432,7 @@ static void amdvi_sysbus_realize(DeviceState *dev, Error **errp)
 static const Property amdvi_properties[] = {
     DEFINE_PROP_BOOL("xtsup", AMDVIState, xtsup, false),
     DEFINE_PROP_STRING("pci-id", AMDVIState, pci_id),
+    DEFINE_PROP_BOOL("dma-remap", AMDVIState, dma_remap, false),
 };
 
 static const VMStateDescription vmstate_amdvi_sysbus = {
-- 
MST