qemu: add ability to set PCI device "rombar" on or off

This patch was made in response to:

  https://bugzilla.redhat.com/show_bug.cgi?id=738095

In short, qemu's default for the rombar setting (which makes the
firmware ROM of a PCI device visible/not on the guest) was previously
0 (not visible), but they recently changed the default to 1
(visible). Unfortunately, there are some PCI devices that fail in the
guest when rombar is 1, so the setting must be exposed in libvirt to
prevent a regression in behavior (it will still require explicitly
setting <rom bar='off'/> in the guest XML).

rombar is forced on/off by adding:

  <rom bar='on|off'/>

inside a <hostdev> element that defines a PCI device. It is currently
ignored for all other types of devices.

At the moment there is no clean method to determine whether or not the
rombar option is supported by QEMU - this patch uses the advice of a
QEMU developer to assume support for qemu-0.12+. There is currently a
patch in the works to put this information in the output of "qemu-kvm
-device pci-assign,?", but of course if we switch to keying off that,
we would lose support for setting rombar on all the versions of qemu
between 0.12 and whatever version gets that patch.

docs/formatdomain.html.in

@@ -1376,6 +1376,7 @@
         <address bus='0x06' slot='0x02' function='0x0'/>
       </source>
       <boot order='1'/>
+      <rom bar='off'/>
     </hostdev>
   </devices>
   ...</pre>
@@ -1407,6 +1408,18 @@
       used together with general boot elements in
       <a href="#elementsOSBIOS">BIOS bootloader</a> section.
       <span class="since">Since 0.8.8</span></dd>
+      <dt><code>rom</code></dt>
+      <dd>The <code>rom</code> element is used to change how a PCI
+        device's ROM is presented to the guest. The <code>bar</code>
+        attribute can be set to "on" or "off", and determines whether
+        or not the device's ROM will be visible in the guest's memory
+        map. (In PCI documentation, the "rombar" setting controls the
+        presence of the Base Address Register for the ROM). If no rom
+        bar is specified, the qemu default will be used (older
+        versions of qemu used a default of "off", while newer qemus
+        have a default of "on"). <span class="since">Since
+        0.9.7</span>
+      </dd>
       <dt><code>address</code></dt>
       <dd>The <code>address</code> element for USB devices has a
       <code>bus</code> and <code>device</code> attribute to specify the

docs/schemas/domaincommon.rng

@@ -2060,6 +2060,17 @@
       <optional>
         <ref name="address"/>
       </optional>
+      <optional>
+        <element name="rom">
+          <attribute name="bar">
+            <choice>
+              <value>on</value>
+              <value>off</value>
+            </choice>
+          </attribute>
+          <empty/>
+        </element>
+      </optional>
     </element>
   </define>
   <define name="usbproduct">

src/conf/domain_conf.c

@@ -443,6 +443,12 @@ VIR_ENUM_IMPL(virDomainHostdevSubsys, VIR_DOMAIN_HOSTDEV_SUBSYS_TYPE_LAST,
               "usb",
               "pci")
 
+VIR_ENUM_IMPL(virDomainPciRombarMode,
+              VIR_DOMAIN_PCI_ROMBAR_LAST,
+              "default",
+              "on",
+              "off")
+
 VIR_ENUM_IMPL(virDomainHub, VIR_DOMAIN_HUB_TYPE_LAST,
               "usb")
 
@@ -5486,6 +5492,20 @@ virDomainHostdevDefParseXML(const xmlNodePtr node,
                 if (virDomainDeviceBootParseXML(cur, &def->bootIndex,
                                                 bootMap))
                     goto error;
+            } else if (xmlStrEqual(cur->name, BAD_CAST "rom")) {
+                char *rombar = virXMLPropString(cur, "bar");
+                if (!rombar) {
+                    virDomainReportError(VIR_ERR_XML_ERROR,
+                                         "%s", _("missing rom bar attribute"));
+                    goto error;
+                }
+                if ((def->rombar = virDomainPciRombarModeTypeFromString(rombar)) <= 0) {
+                    virDomainReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                                         _("unknown rom bar value '%s'"), rombar);
+                    VIR_FREE(rombar);
+                    goto error;
+                }
+                VIR_FREE(rombar);
             } else {
                 virDomainReportError(VIR_ERR_INTERNAL_ERROR,
                                      _("unknown node %s"), cur->name);
@@ -10388,6 +10408,18 @@ virDomainHostdevDefFormat(virBufferPtr buf,
     if (virDomainDeviceInfoFormat(buf, &def->info, flags) < 0)
         return -1;
 
+    if (def->rombar) {
+        const char *rombar
+            = virDomainPciRombarModeTypeToString(def->rombar);
+        if (!rombar) {
+            virDomainReportError(VIR_ERR_INTERNAL_ERROR,
+                                 _("unexpected rom bar value %d"),
+                                 def->rombar);
+            return -1;
+        }
+        virBufferAsprintf(buf, "      <rom bar='%s'/>\n", rombar);
+    }
+
     virBufferAddLit(buf, "    </hostdev>\n");
 
     return 0;

src/conf/domain_conf.h

@@ -937,6 +937,14 @@ enum virDomainHostdevSubsysType {
     VIR_DOMAIN_HOSTDEV_SUBSYS_TYPE_LAST
 };
 
+enum virDomainPciRombarMode {
+    VIR_DOMAIN_PCI_ROMBAR_DEFAULT = 0,
+    VIR_DOMAIN_PCI_ROMBAR_ON,
+    VIR_DOMAIN_PCI_ROMBAR_OFF,
+
+    VIR_DOMAIN_PCI_ROMBAR_LAST
+};
+
 typedef struct _virDomainHostdevDef virDomainHostdevDef;
 typedef virDomainHostdevDef *virDomainHostdevDefPtr;
 struct _virDomainHostdevDef {
@@ -965,6 +973,7 @@ struct _virDomainHostdevDef {
     } source;
     int bootIndex;
     virDomainDeviceInfo info; /* Guest address */
+    int rombar;               /* enum virDomainPciRombarMode */
 };
 
 enum virDomainRedirdevBus {
@@ -1856,6 +1865,7 @@ VIR_ENUM_DECL(virDomainWatchdogAction)
 VIR_ENUM_DECL(virDomainVideo)
 VIR_ENUM_DECL(virDomainHostdevMode)
 VIR_ENUM_DECL(virDomainHostdevSubsys)
+VIR_ENUM_DECL(virDomainPciRombarMode)
 VIR_ENUM_DECL(virDomainHub)
 VIR_ENUM_DECL(virDomainRedirdevBus)
 VIR_ENUM_DECL(virDomainInput)

src/libvirt_private.syms

@@ -385,6 +385,8 @@ virDomainObjUnlock;
 virDomainObjUnref;
 virDomainPausedReasonTypeFromString;
 virDomainPausedReasonTypeToString;
+virDomainPciRombarModeTypeFromString;
+virDomainPciRombarModeTypeToString;
 virDomainRedirdevBusTypeFromString;
 virDomainRedirdevBusTypeToString;
 virDomainRemoveInactive;

src/qemu/qemu_capabilities.c

@@ -139,6 +139,7 @@ VIR_ENUM_IMPL(qemuCaps, QEMU_CAPS_LAST,
               "no-shutdown",
 
               "cache-unsafe", /* 75 */
+              "rombar",
     );
 
 struct qemu_feature_flags {
@@ -1063,6 +1064,19 @@ qemuCapsComputeCmdFlags(const char *help,
 
     if (version >= 13000)
         qemuCapsSet(flags, QEMU_CAPS_PCI_MULTIFUNCTION);
+
+    /* Although very new versions of qemu advertise the presence of
+     * the rombar option in the output of "qemu -device pci-assign,?",
+     * this advertisement was added to the code long after the option
+     * itself. According to qemu developers, though, rombar is
+     * available in all qemu binaries from release 0.12 onward.
+     * Setting the capability this way makes it available in more
+     * cases where it might be needed, and shouldn't cause any false
+     * positives (in the case that it did, qemu would produce an error
+     * log and refuse to start, so it would be immediately obvious).
+     */
+    if (version >= 12000)
+        qemuCapsSet(flags, QEMU_CAPS_PCI_ROMBAR);
 }
 
 /* We parse the output of 'qemu -help' to get the QEMU

src/qemu/qemu_capabilities.h

@@ -113,6 +113,7 @@ enum qemuCapsFlags {
     QEMU_CAPS_NO_SHUTDOWN       = 74, /* usable -no-shutdown */
 
     QEMU_CAPS_DRIVE_CACHE_UNSAFE = 75, /* Is cache=unsafe supported? */
+    QEMU_CAPS_PCI_ROMBAR         = 76, /* -device rombar=0|1 */
 
     QEMU_CAPS_LAST,                   /* this must always be the last item */
 };

src/qemu/qemu_command.c

@@ -2369,6 +2369,25 @@ qemuBuildPCIHostdevDevStr(virDomainHostdevDefPtr dev, const char *configfd,
     if (qemuBuildDeviceAddressStr(&buf, &dev->info, qemuCaps) < 0)
         goto error;
 
+    if (dev->rombar) {
+        if (!qemuCapsGet(qemuCaps, QEMU_CAPS_PCI_ROMBAR)) {
+            qemuReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                            "%s", _("rombar not supported in this QEMU binary"));
+            goto error;
+        }
+
+        switch (dev->rombar) {
+        case VIR_DOMAIN_PCI_ROMBAR_OFF:
+            virBufferAddLit(&buf, ",rombar=0");
+            break;
+        case VIR_DOMAIN_PCI_ROMBAR_ON:
+            virBufferAddLit(&buf, ",rombar=1");
+            break;
+        default:
+            break;
+        }
+    }
+
     if (virBufferError(&buf)) {
         virReportOOMError();
         goto error;

tests/qemuhelptest.c

@@ -314,7 +314,8 @@ mymain(void)
             QEMU_CAPS_VGA_NONE,
             QEMU_CAPS_MIGRATE_QEMU_FD,
             QEMU_CAPS_DRIVE_AIO,
-            QEMU_CAPS_NO_SHUTDOWN);
+            QEMU_CAPS_NO_SHUTDOWN,
+            QEMU_CAPS_PCI_ROMBAR);
     DO_TEST("qemu-kvm-0.12.1.2-rhel60", 12001, 1, 0,
             QEMU_CAPS_VNC_COLON,
             QEMU_CAPS_NO_REBOOT,
@@ -359,7 +360,8 @@ mymain(void)
             QEMU_CAPS_PIIX3_USB_UHCI,
             QEMU_CAPS_PIIX4_USB_UHCI,
             QEMU_CAPS_USB_HUB,
-            QEMU_CAPS_NO_SHUTDOWN);
+            QEMU_CAPS_NO_SHUTDOWN,
+            QEMU_CAPS_PCI_ROMBAR);
     DO_TEST("qemu-kvm-0.12.3", 12003, 1, 0,
             QEMU_CAPS_VNC_COLON,
             QEMU_CAPS_NO_REBOOT,
@@ -397,7 +399,8 @@ mymain(void)
             QEMU_CAPS_VGA_NONE,
             QEMU_CAPS_MIGRATE_QEMU_FD,
             QEMU_CAPS_DRIVE_AIO,
-            QEMU_CAPS_NO_SHUTDOWN);
+            QEMU_CAPS_NO_SHUTDOWN,
+            QEMU_CAPS_PCI_ROMBAR);
     DO_TEST("qemu-kvm-0.13.0", 13000, 1, 0,
             QEMU_CAPS_VNC_COLON,
             QEMU_CAPS_NO_REBOOT,
@@ -451,7 +454,8 @@ mymain(void)
             QEMU_CAPS_VT82C686B_USB_UHCI,
             QEMU_CAPS_PCI_OHCI,
             QEMU_CAPS_USB_HUB,
-            QEMU_CAPS_NO_SHUTDOWN);
+            QEMU_CAPS_NO_SHUTDOWN,
+            QEMU_CAPS_PCI_ROMBAR);
     DO_TEST("qemu-kvm-0.12.1.2-rhel61", 12001, 1, 0,
             QEMU_CAPS_VNC_COLON,
             QEMU_CAPS_NO_REBOOT,
@@ -501,7 +505,8 @@ mymain(void)
             QEMU_CAPS_PIIX3_USB_UHCI,
             QEMU_CAPS_PIIX4_USB_UHCI,
             QEMU_CAPS_USB_HUB,
-            QEMU_CAPS_NO_SHUTDOWN);
+            QEMU_CAPS_NO_SHUTDOWN,
+            QEMU_CAPS_PCI_ROMBAR);
 
     return ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE;
 }

tests/qemuxml2argvdata/qemuxml2argv-hostdev-pci-rombar.args

+LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test /usr/bin/qemu -S -M \
+pc -m 214 -smp 1 -nographic -nodefconfig -nodefaults -monitor \
+unix:/tmp/test-monitor,server,nowait -no-acpi -boot c -hda \
+/dev/HostVG/QEMUGuest2 -usb -device pci-assign,host=06:12.5,id=hostdev0,\
+bus=pci.0,addr=0x3,rombar=0 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x4

tests/qemuxml2argvdata/qemuxml2argv-hostdev-pci-rombar.xml

+<domain type='qemu'>
+  <name>QEMUGuest2</name>
+  <uuid>c7a5fdbd-edaf-9466-926a-d65c16db1809</uuid>
+  <memory>219100</memory>
+  <currentMemory>219100</currentMemory>
+  <vcpu>1</vcpu>
+  <os>
+    <type arch='i686' machine='pc'>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</emulator>
+    <disk type='block' device='disk'>
+      <source dev='/dev/HostVG/QEMUGuest2'/>
+      <target dev='hda' bus='ide'/>
+    </disk>
+    <hostdev mode='subsystem' type='pci' managed='yes'>
+      <source>
+        <address domain='0x0000' bus='0x06' slot='0x12' function='0x5'/>
+      </source>
+      <rom bar='off'/>
+    </hostdev>
+    <memballoon model='virtio'/>
+  </devices>
+</domain>