conf: add xen specific feature: e820_host

e820_host is a Xen-specific option, only available for PV domains, that
provides the domain a virtual e820 memory map based on the host one. It
is enabled with a new Xen hypervisor feature, e.g.

  <features>
    <xen>
      <e820_host state='on'/>
    </xen>
  </features>

e820_host is required when using PCI passthrough and is generally
considered safe for any PV kernel. e820_host is silently ignored if set
in HVM domain configuration. See xl.cfg(5) man page in the Xen
documentation for more details.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Reviewed-by: Jim Fehlig <jfehlig@suse.com>

docs/formatdomain.html.in

@@ -2061,6 +2061,9 @@
     <hidden state='on'/>
     <hint-dedicated state='on'/>
   </kvm>
+  <xen>
+    <e820_host state='on'/>
+  </xen>
   <pvspinlock state='on'/>
   <gic version='2'/>
   <ioapic driver='qemu'/>
@@ -2242,6 +2245,23 @@
         </tr>
       </table>
       </dd>
+      <dt><code>xen</code></dt>
+      <dd>Various features to change the behavior of the Xen hypervisor.
+      <table class="top_table">
+        <tr>
+          <th>Feature</th>
+          <th>Description</th>
+          <th>Value</th>
+          <th>Since</th>
+        </tr>
+        <tr>
+          <td>e820_host</td>
+          <td>Expose the host e820 to the guest (PV only)</td>
+          <td>on, off</td>
+          <td><span class="since">6.3.0</span></td>
+        </tr>
+      </table>
+      </dd>
       <dt><code>pmu</code></dt>
       <dd>Depending on the <code>state</code> attribute (values <code>on</code>,
         <code>off</code>, default <code>on</code>) enable or disable the

docs/schemas/domaincommon.rng

@@ -5348,6 +5348,9 @@
           <optional>
             <ref name="kvm"/>
           </optional>
+          <optional>
+            <ref name="xen"/>
+          </optional>
           <optional>
             <element name="privnet">
               <empty/>
@@ -6337,6 +6340,19 @@
     </element>
   </define>
 
+  <!-- Optional Xen features -->
+  <define name="xen">
+    <element name="xen">
+      <interleave>
+        <optional>
+          <element name="e820_host">
+            <ref name="featurestate"/>
+          </element>
+        </optional>
+      </interleave>
+    </element>
+  </define>
+
   <!-- Optional capabilities features -->
   <define name="capabilities">
     <element name="capabilities">

src/conf/domain_conf.c

@@ -173,6 +173,7 @@ VIR_ENUM_IMPL(virDomainFeature,
               "nested-hv",
               "msrs",
               "ccf-assist",
+              "xen",
 );
 
 VIR_ENUM_IMPL(virDomainCapabilitiesPolicy,
@@ -206,6 +207,11 @@ VIR_ENUM_IMPL(virDomainKVM,
               "hint-dedicated",
 );
 
+VIR_ENUM_IMPL(virDomainXen,
+              VIR_DOMAIN_XEN_LAST,
+              "e820_host"
+);
+
 VIR_ENUM_IMPL(virDomainMsrsUnknown,
               VIR_DOMAIN_MSRS_UNKNOWN_LAST,
               "ignore",
@@ -20862,6 +20868,7 @@ virDomainDefParseXML(xmlDocPtr xml,
         case VIR_DOMAIN_FEATURE_HYPERV:
         case VIR_DOMAIN_FEATURE_KVM:
         case VIR_DOMAIN_FEATURE_MSRS:
+        case VIR_DOMAIN_FEATURE_XEN:
             def->features[val] = VIR_TRISTATE_SWITCH_ON;
             break;
 
@@ -21172,6 +21179,51 @@ virDomainDefParseXML(xmlDocPtr xml,
         VIR_FREE(nodes);
     }
 
+    if (def->features[VIR_DOMAIN_FEATURE_XEN] == VIR_TRISTATE_SWITCH_ON) {
+        int feature;
+        int value;
+        if ((n = virXPathNodeSet("./features/xen/*", ctxt, &nodes)) < 0)
+            goto error;
+
+        for (i = 0; i < n; i++) {
+            feature = virDomainXenTypeFromString((const char *)nodes[i]->name);
+            if (feature < 0) {
+                virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                               _("unsupported Xen feature: %s"),
+                               nodes[i]->name);
+                goto error;
+            }
+
+            switch ((virDomainXen) feature) {
+                case VIR_DOMAIN_XEN_E820_HOST:
+                    if (!(tmp = virXMLPropString(nodes[i], "state"))) {
+                        virReportError(VIR_ERR_XML_ERROR,
+                                       _("missing 'state' attribute for "
+                                         "Xen feature '%s'"),
+                                       nodes[i]->name);
+                        goto error;
+                    }
+
+                    if ((value = virTristateSwitchTypeFromString(tmp)) < 0) {
+                        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                                       _("invalid value of state argument "
+                                         "for Xen feature '%s'"),
+                                       nodes[i]->name);
+                        goto error;
+                    }
+
+                    VIR_FREE(tmp);
+                    def->xen_features[feature] = value;
+                    break;
+
+                /* coverity[dead_error_begin] */
+                case VIR_DOMAIN_XEN_LAST:
+                    break;
+            }
+        }
+        VIR_FREE(nodes);
+    }
+
     if (def->features[VIR_DOMAIN_FEATURE_SMM] == VIR_TRISTATE_SWITCH_ON) {
         int rv = virDomainParseScaledValue("string(./features/smm/tseg)",
                                            "string(./features/smm/tseg/@unit)",
@@ -23173,6 +23225,7 @@ virDomainDefFeaturesCheckABIStability(virDomainDefPtr src,
         case VIR_DOMAIN_FEATURE_PRIVNET:
         case VIR_DOMAIN_FEATURE_HYPERV:
         case VIR_DOMAIN_FEATURE_KVM:
+        case VIR_DOMAIN_FEATURE_XEN:
         case VIR_DOMAIN_FEATURE_PVSPINLOCK:
         case VIR_DOMAIN_FEATURE_PMU:
         case VIR_DOMAIN_FEATURE_VMPORT:
@@ -23344,6 +23397,30 @@ virDomainDefFeaturesCheckABIStability(virDomainDefPtr src,
         }
     }
 
+    /* xen */
+    if (src->features[VIR_DOMAIN_FEATURE_XEN] == VIR_TRISTATE_SWITCH_ON) {
+        for (i = 0; i < VIR_DOMAIN_XEN_LAST; i++) {
+            switch ((virDomainXen) i) {
+            case VIR_DOMAIN_XEN_E820_HOST:
+                if (src->xen_features[i] != dst->xen_features[i]) {
+                    virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                                   _("State of Xen feature '%s' differs: "
+                                     "source: '%s', destination: '%s'"),
+                                   virDomainXenTypeToString(i),
+                                   virTristateSwitchTypeToString(src->xen_features[i]),
+                                   virTristateSwitchTypeToString(dst->xen_features[i]));
+                    return false;
+                }
+
+                break;
+
+            /* coverity[dead_error_begin] */
+            case VIR_DOMAIN_XEN_LAST:
+                break;
+            }
+        }
+    }
+
     /* kvm */
     if (src->features[VIR_DOMAIN_FEATURE_KVM] == VIR_TRISTATE_SWITCH_ON) {
         for (i = 0; i < VIR_DOMAIN_KVM_LAST; i++) {
@@ -28963,6 +29040,31 @@ virDomainDefFormatFeatures(virBufferPtr buf,
             virBufferAddLit(&childBuf, "</kvm>\n");
             break;
 
+        case VIR_DOMAIN_FEATURE_XEN:
+            if (def->features[i] != VIR_TRISTATE_SWITCH_ON)
+                break;
+
+            virBufferAddLit(&childBuf, "<xen>\n");
+            virBufferAdjustIndent(&childBuf, 2);
+            for (j = 0; j < VIR_DOMAIN_XEN_LAST; j++) {
+                switch ((virDomainXen) j) {
+                case VIR_DOMAIN_XEN_E820_HOST:
+                    if (def->xen_features[j])
+                        virBufferAsprintf(&childBuf, "<%s state='%s'/>\n",
+                                          virDomainXenTypeToString(j),
+                                          virTristateSwitchTypeToString(
+                                              def->xen_features[j]));
+                    break;
+
+                /* coverity[dead_error_begin] */
+                case VIR_DOMAIN_XEN_LAST:
+                    break;
+                }
+            }
+            virBufferAdjustIndent(&childBuf, -2);
+            virBufferAddLit(&childBuf, "</xen>\n");
+            break;
+
         case VIR_DOMAIN_FEATURE_CAPABILITIES:
             for (j = 0; j < VIR_DOMAIN_PROCES_CAPS_FEATURE_LAST; j++) {
                 if (def->caps_features[j] != VIR_TRISTATE_SWITCH_ABSENT)

src/conf/domain_conf.h

@@ -1814,6 +1814,7 @@ typedef enum {
     VIR_DOMAIN_FEATURE_NESTED_HV,
     VIR_DOMAIN_FEATURE_MSRS,
     VIR_DOMAIN_FEATURE_CCF_ASSIST,
+    VIR_DOMAIN_FEATURE_XEN,
 
     VIR_DOMAIN_FEATURE_LAST
 } virDomainFeature;
@@ -1859,6 +1860,12 @@ typedef enum {
     VIR_DOMAIN_MSRS_UNKNOWN_LAST
 } virDomainMsrsUnknown;
 
+typedef enum {
+    VIR_DOMAIN_XEN_E820_HOST = 0,
+
+    VIR_DOMAIN_XEN_LAST
+} virDomainXen;
+
 typedef enum {
     VIR_DOMAIN_CAPABILITIES_POLICY_DEFAULT = 0,
     VIR_DOMAIN_CAPABILITIES_POLICY_ALLOW,
@@ -2484,6 +2491,7 @@ struct _virDomainDef {
     int hyperv_features[VIR_DOMAIN_HYPERV_LAST];
     int kvm_features[VIR_DOMAIN_KVM_LAST];
     int msrs_features[VIR_DOMAIN_MSRS_LAST];
+    int xen_features[VIR_DOMAIN_XEN_LAST];
     unsigned int hyperv_spinlocks;
     int hyperv_stimer_direct;
     virGICVersion gic_version;
@@ -3529,6 +3537,7 @@ VIR_ENUM_DECL(virDomainGraphicsSpiceMouseMode);
 VIR_ENUM_DECL(virDomainGraphicsVNCSharePolicy);
 VIR_ENUM_DECL(virDomainHyperv);
 VIR_ENUM_DECL(virDomainKVM);
+VIR_ENUM_DECL(virDomainXen);
 VIR_ENUM_DECL(virDomainMsrsUnknown);
 VIR_ENUM_DECL(virDomainRNGModel);
 VIR_ENUM_DECL(virDomainRNGBackend);

src/qemu/qemu_validate.c

@@ -302,6 +302,7 @@ qemuValidateDomainDefFeatures(const virDomainDef *def,
             }
             break;
 
+        case VIR_DOMAIN_FEATURE_XEN:
         case VIR_DOMAIN_FEATURE_ACPI:
         case VIR_DOMAIN_FEATURE_PAE:
         case VIR_DOMAIN_FEATURE_HAP: