conf: add caching_mode attribute to iommu device

Add a new attribute to control the caching mode.

https://bugzilla.redhat.com/show_bug.cgi?id=1427005

docs/formatdomain.html.in

@@ -7427,6 +7427,15 @@ qemu-kvm -net nic,model=? /dev/null
               <span class="since">Since 3.4.0</span> (QEMU/KVM only)
             </p>
           </dd>
+          <dt><code>caching_mode</code></dt>
+          <dd>
+            <p>
+              The <code>caching_mode</code> attribute with possible values
+              <code>on</code> and <code>off</code> can be used to
+              turn on the VT-d caching mode (useful for assigned devices).
+              <span class="since">Since 3.4.0</span> (QEMU/KVM only)
+            </p>
+          </dd>
         </dl>
       </dd>
     </dl>

docs/schemas/domaincommon.rng

@@ -3954,6 +3954,11 @@
               <ref name="virOnOff"/>
             </attribute>
           </optional>
+          <optional>
+            <attribute name="caching_mode">
+              <ref name="virOnOff"/>
+            </attribute>
+          </optional>
         </element>
       </optional>
     </element>

src/conf/domain_conf.c

@@ -14176,6 +14176,15 @@ virDomainIOMMUDefParseXML(xmlNodePtr node,
         iommu->intremap = val;
     }
 
+    VIR_FREE(tmp);
+    if ((tmp = virXPathString("string(./driver/@caching_mode)", ctxt))) {
+        if ((val = virTristateSwitchTypeFromString(tmp)) < 0) {
+            virReportError(VIR_ERR_XML_ERROR, _("unknown caching_mode value: %s"), tmp);
+            goto cleanup;
+        }
+        iommu->caching_mode = val;
+    }
+
     ret = iommu;
     iommu = NULL;
 
@@ -24143,9 +24152,18 @@ virDomainIOMMUDefFormat(virBufferPtr buf,
 
     virBufferAdjustIndent(&childBuf, virBufferGetIndent(buf, false) + 2);
 
-    if (iommu->intremap != VIR_TRISTATE_SWITCH_ABSENT) {
-        virBufferAsprintf(&childBuf, "<driver intremap='%s'/>\n",
-                          virTristateSwitchTypeToString(iommu->intremap));
+    if (iommu->intremap != VIR_TRISTATE_SWITCH_ABSENT ||
+        iommu->caching_mode != VIR_TRISTATE_SWITCH_ABSENT) {
+        virBufferAddLit(&childBuf, "<driver");
+        if (iommu->intremap != VIR_TRISTATE_SWITCH_ABSENT) {
+            virBufferAsprintf(&childBuf, " intremap='%s'",
+                              virTristateSwitchTypeToString(iommu->intremap));
+        }
+        if (iommu->caching_mode != VIR_TRISTATE_SWITCH_ABSENT) {
+            virBufferAsprintf(&childBuf, " caching_mode='%s'",
+                              virTristateSwitchTypeToString(iommu->caching_mode));
+        }
+        virBufferAddLit(&childBuf, "/>\n");
     }
 
     virBufferAsprintf(buf, "<iommu model='%s'",

src/conf/domain_conf.h

@@ -2210,6 +2210,7 @@ typedef enum {
 struct _virDomainIOMMUDef {
     virDomainIOMMUModel model;
     virTristateSwitch intremap;
+    virTristateSwitch caching_mode;
 };
 /*
  * Guest VM main configuration

tests/qemuxml2argvdata/qemuxml2argv-intel-iommu-caching-mode.xml

+<domain type='qemu'>
+  <name>QEMUGuest1</name>
+  <uuid>c7a5fdbd-edaf-9455-926a-d65c16db1809</uuid>
+  <memory unit='KiB'>219100</memory>
+  <currentMemory unit='KiB'>219100</currentMemory>
+  <vcpu placement='static'>1</vcpu>
+  <os>
+    <type arch='x86_64' machine='q35'>hvm</type>
+    <boot dev='hd'/>
+  </os>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu-system-x86_64</emulator>
+    <controller type='pci' index='0' model='pcie-root'/>
+    <controller type='pci' index='1' model='dmi-to-pci-bridge'>
+      <model name='i82801b11-bridge'/>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x1e' function='0x0'/>
+    </controller>
+    <controller type='pci' index='2' model='pci-bridge'>
+      <model name='pci-bridge'/>
+      <target chassisNr='2'/>
+      <address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
+    </controller>
+    <controller type='pci' index='3' model='pcie-root-port'>
+      <model name='ioh3420'/>
+      <target chassis='3' port='0x10'/>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
+    </controller>
+    <controller type='sata' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x1f' function='0x2'/>
+    </controller>
+    <controller type='usb' index='0' model='ich9-ehci1'>
+      <address type='pci' domain='0x0000' bus='0x02' slot='0x02' function='0x7'/>
+    </controller>
+    <interface type='user'>
+      <mac address='52:54:00:ab:0c:5c'/>
+      <model type='rtl8139'/>
+      <address type='pci' domain='0x0000' bus='0x02' slot='0x01' function='0x0'/>
+    </interface>
+    <input type='mouse' bus='ps2'/>
+    <input type='keyboard' bus='ps2'/>
+    <memballoon model='none'/>
+    <iommu model='intel'>
+      <driver intremap='on' caching_mode='on'/>
+    </iommu>
+  </devices>
+</domain>

tests/qemuxml2xmloutdata/qemuxml2xmlout-intel-iommu-caching-mode.xml

+../qemuxml2argvdata/qemuxml2argv-intel-iommu-caching-mode.xml
\ No newline at end of file

tests/qemuxml2xmltest.c

@@ -1123,6 +1123,7 @@ mymain(void)
             QEMU_CAPS_MACHINE_OPT,
             QEMU_CAPS_MACHINE_IOMMU);
     DO_TEST("intel-iommu-ioapic", NONE);
+    DO_TEST("intel-iommu-caching-mode", NONE);
 
     DO_TEST("cpu-check-none", NONE);
     DO_TEST("cpu-check-partial", NONE);