Re: [PATCH v3 1/3] conf: Support multiple device-pluggable smmuv3 IOMMUs

18 Nov 2025

On a Wednesday in 2025, Nathan Chen via Devel wrote:
...
Add support for parsing multiple IOMMU devices from
the VM definition when "smmuv3" is the IOMMU model.
Signed-off-by: Nathan Chen <nathanc@nvidia.com>
---
src/conf/domain_conf.c            |  84 +++++++++++++++-----
src/conf/domain_conf.h            |   9 ++-
src/conf/domain_validate.c        |  33 +++++---
src/conf/schemas/domaincommon.rng |   4 +-
src/libvirt_private.syms          |   2 +
src/qemu/qemu_alias.c             |  15 ++--
src/qemu/qemu_command.c           | 127 +++++++++++++++---------------
src/qemu/qemu_domain.c            |   2 +-
src/qemu/qemu_domain_address.c    |   5 +-
src/qemu/qemu_driver.c            |   8 +-
src/qemu/qemu_postparse.c         |  11 +--
src/qemu/qemu_validate.c          |   2 +-
12 files changed, 184 insertions(+), 118 deletions(-)

diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index c56c321a6e..97fe4267ec 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -6244,84 +6244,85 @@ qemuBuildIOMMUCommandLine(virCommand *cmd,
                          const virDomainDef *def,
                          virQEMUCaps *qemuCaps)
{
+    size_t i;
    g_autoptr(virJSONValue) props = NULL;
    g_autoptr(virJSONValue) wrapperProps = NULL;
-    const virDomainIOMMUDef *iommu = def->iommu;

...
-    if (!iommu)
+    if (def->niommus == 0)
        return 0;
This condition is no longer needed - the for cycle already checks
def->niommus.
...
-    switch (iommu->model) {
-    case VIR_DOMAIN_IOMMU_MODEL_INTEL:
-        if (virJSONValueObjectAdd(&props,
-                                  "s:driver", "intel-iommu",
-                                  "s:id", iommu->info.alias,
-                                  "S:intremap", qemuOnOffAuto(iommu->intremap),
-                                  "T:caching-mode", iommu->caching_mode,
-                                  "S:eim", qemuOnOffAuto(iommu->eim),
-                                  "T:device-iotlb", iommu->iotlb,
-                                  "z:aw-bits", iommu->aw_bits,
-                                  "T:dma-translation", iommu->dma_translation,
-                                  NULL) < 0)
-            return -1;
+    for (i = 0; i < def->niommus; i++) {
+        virDomainIOMMUDef *iommu = def->iommus[i];
+        switch (iommu->model) {
+        case VIR_DOMAIN_IOMMU_MODEL_INTEL:
+            if (virJSONValueObjectAdd(&props,
+                                      "s:driver", "intel-iommu",
+                                      "s:id", iommu->info.alias,
+                                      "S:intremap", qemuOnOffAuto(iommu->intremap),
+                                      "T:caching-mode", iommu->caching_mode,
+                                      "S:eim", qemuOnOffAuto(iommu->eim),
+                                      "T:device-iotlb", iommu->iotlb,
+                                      "z:aw-bits", iommu->aw_bits,
+                                      "T:dma-translation", iommu->dma_translation,
+                                      NULL) < 0)
+                return -1;
-        if (qemuBuildDeviceCommandlineFromJSON(cmd, props, def, qemuCaps) < 0)
-            return -1;
+            if (qemuBuildDeviceCommandlineFromJSON(cmd, props, def, qemuCaps) < 0)
+                return -1;
-        return 0;
+            return 0;
break; instead of return; - even though there can practially be only one device,
the function iterates through all of them and should not exit early
...
+        case VIR_DOMAIN_IOMMU_MODEL_VIRTIO:
+            if (virJSONValueObjectAdd(&props,
+                                      "s:driver", "virtio-iommu",
+                                      "s:id", iommu->info.alias,
+                                      NULL) < 0) {
+                return -1;
+            }
-    case VIR_DOMAIN_IOMMU_MODEL_VIRTIO:
-        if (virJSONValueObjectAdd(&props,
-                                  "s:driver", "virtio-iommu",
-                                  "s:id", iommu->info.alias,
-                                  NULL) < 0) {
-            return -1;
-        }
+            if (qemuBuildDeviceAddressProps(props, def, &iommu->info) < 0)
+                return -1;
-        if (qemuBuildDeviceAddressProps(props, def, &iommu->info) < 0)
-            return -1;
+            if (qemuBuildDeviceCommandlineFromJSON(cmd, props, def, qemuCaps) < 0)
+                return -1;
-        if (qemuBuildDeviceCommandlineFromJSON(cmd, props, def, qemuCaps) < 0)
-            return -1;
+            return 0;
Same here
...
+        case VIR_DOMAIN_IOMMU_MODEL_SMMUV3:
+            /* There is no -device for SMMUv3, so nothing to be done here */
+            return 0;
And here.
...
-        return 0;
+        case VIR_DOMAIN_IOMMU_MODEL_AMD:
+            if (virJSONValueObjectAdd(&wrapperProps,
+                                      "s:driver", "AMDVI-PCI",
+                                      "s:id", iommu->info.alias,
+                                      NULL) < 0)
+                return -1;
-    case VIR_DOMAIN_IOMMU_MODEL_SMMUV3:
-        /* There is no -device for SMMUv3, so nothing to be done here */
-        return 0;
+            if (qemuBuildDeviceAddressProps(wrapperProps, def, &iommu->info) < 0)
+                return -1;
-    case VIR_DOMAIN_IOMMU_MODEL_AMD:
-        if (virJSONValueObjectAdd(&wrapperProps,
-                                  "s:driver", "AMDVI-PCI",
-                                  "s:id", iommu->info.alias,
-                                  NULL) < 0)
-            return -1;
+            if (qemuBuildDeviceCommandlineFromJSON(cmd, wrapperProps, def, qemuCaps) < 0)
+                return -1;
-        if (qemuBuildDeviceAddressProps(wrapperProps, def, &iommu->info) < 0)
-            return -1;
+            if (virJSONValueObjectAdd(&props,
+                                      "s:driver", "amd-iommu",
+                                      "s:pci-id", iommu->info.alias,
+                                      "S:intremap", qemuOnOffAuto(iommu->intremap),
+                                      "T:pt", iommu->pt,
+                                      "T:xtsup", iommu->xtsup,
+                                      "T:device-iotlb", iommu->iotlb,
+                                      NULL) < 0)
+                return -1;
-        if (qemuBuildDeviceCommandlineFromJSON(cmd, wrapperProps, def, qemuCaps) < 0)
-            return -1;
+            if (qemuBuildDeviceCommandlineFromJSON(cmd, props, def, qemuCaps) < 0)
+                return -1;
-        if (virJSONValueObjectAdd(&props,
-                                  "s:driver", "amd-iommu",
-                                  "s:pci-id", iommu->info.alias,
-                                  "S:intremap", qemuOnOffAuto(iommu->intremap),
-                                  "T:pt", iommu->pt,
-                                  "T:xtsup", iommu->xtsup,
-                                  "T:device-iotlb", iommu->iotlb,
-                                  NULL) < 0)
-            return -1;
+            return 0;
Here too.
...
-        if (qemuBuildDeviceCommandlineFromJSON(cmd, props, def, qemuCaps) < 0)
+        case VIR_DOMAIN_IOMMU_MODEL_LAST:
+        default:
+            virReportEnumRangeError(virDomainIOMMUModel, iommu->model);
            return -1;
-
-        return 0;
-
-    case VIR_DOMAIN_IOMMU_MODEL_LAST:
-    default:
-        virReportEnumRangeError(virDomainIOMMUModel, iommu->model);
-        return -1;
+        }
    }
return 0;
diff --git a/src/qemu/qemu_postparse.c b/src/qemu/qemu_postparse.c
index fd27f8be27..3b417ea5d0 100644
--- a/src/qemu/qemu_postparse.c
+++ b/src/qemu/qemu_postparse.c
@@ -1470,7 +1470,7 @@ qemuDomainDefAddDefaultDevices(virQEMUDriver *driver,
        }
    }
-    if (addIOMMU && !def->iommu &&
+    if (addIOMMU && !def->iommus && def->niommus == 0 &&
        virQEMUCapsGet(qemuCaps, QEMU_CAPS_DEVICE_INTEL_IOMMU) &&
        virQEMUCapsGet(qemuCaps, QEMU_CAPS_INTEL_IOMMU_INTREMAP) &&
        virQEMUCapsGet(qemuCaps, QEMU_CAPS_INTEL_IOMMU_EIM)) {
@@ -1482,7 +1482,8 @@ qemuDomainDefAddDefaultDevices(virQEMUDriver *driver,
        iommu->intremap = VIR_TRISTATE_SWITCH_ON;
        iommu->eim = VIR_TRISTATE_SWITCH_ON;
-        def->iommu = g_steal_pointer(&iommu);
+        def->iommus = g_new0(virDomainIOMMUDef *, 1);
+        def->iommus[def->niommus++] = g_steal_pointer(&iommu);
    }
if (qemuDomainDefAddDefaultAudioBackend(driver, def) < 0)
@@ -1558,9 +1559,9 @@ qemuDomainDefEnableDefaultFeatures(virDomainDef *def,
     * domain already has IOMMU without inremap. This will be fixed in
     * qemuDomainIOMMUDefPostParse() but there domain definition can't be
     * modified so change it now. */
-    if (def->iommu &&
-        (def->iommu->intremap == VIR_TRISTATE_SWITCH_ON ||
-         qemuDomainNeedsIOMMUWithEIM(def)) &&
+    if (def->iommus && def->niommus == 1 &&
+        (def->iommus[0]->intremap == VIR_TRISTATE_SWITCH_ON ||
+        qemuDomainNeedsIOMMUWithEIM(def)) &&
qemuDomainNeedsIOMMUWithEIM was aligned properly originally.
...
def->features[VIR_DOMAIN_FEATURE_IOAPIC] == VIR_DOMAIN_IOAPIC_NONE) {
        def->features[VIR_DOMAIN_FEATURE_IOAPIC] = VIR_DOMAIN_IOAPIC_QEMU;
    }
Reviewed-by: Ján Tomko <jtomko@redhat.com>

Jano

    