conf: Introduce @memReserve to <controller/>

There are PCI devices with pretty large non-prefetchable memory,
for instance:

  Memory at 9d800000 (64-bit, non-prefetchable) [size=8M]
  Memory at a6800000 (64-bit, non-prefetchable) [size=16K]

For cold plugged devices this is not a problem, because firmware
sets PCI controllers in a way that make devices behind them just
work. Problem arises if such PCI device is to be hot plugged.
Since the PCI device wasn't present at cold boot, firmware could
not take it into calculations and the amount of reserved memory
is not sufficient.

Introduce a know that allows users overriding value computed by
FW and thus allow hot plug of such PCI devices.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>

docs/formatdomain.rst

@@ -4153,6 +4153,12 @@ generated by libvirt. :since:`Since 1.2.19 (QEMU only)`.
 ``index``
    pci-root controllers for pSeries guests use this attribute to record the
    order they will show up in the guest. :since:`Since 3.6.0`
+``memReserve``
+   Some PCI devices have non-prefetchable memory bar larger than 2MiB. Use this
+   attribute to override value computed by firmware and thus make controller
+   reserve more memory (in KiB) so that such PCI device can be hot plugged.
+   For cold plugged PCI devices, the firmware will automatically reserve the
+   correct amount of memory. :since:`Since 10.3.0`
 
 For machine types which provide an implicit PCI bus, the pci-root controller
 with index=0 is auto-added and required to use PCI devices. pci-root has no

src/conf/domain_conf.c

@@ -8528,6 +8528,11 @@ virDomainControllerDefParseXML(virDomainXMLOption *xmlopt,
                               &def->opts.pciopts.targetIndex,
                               def->opts.pciopts.targetIndex) < 0)
                 return NULL;
+
+            if (virXMLPropULongLong(targetNodes[0], "memReserve", 0,
+                                    VIR_XML_PROP_NONZERO,
+                                    &def->opts.pciopts.memReserve) < 0)
+                return NULL;
         }
     }
 
@@ -23095,6 +23100,10 @@ virDomainControllerDefFormatPCI(virBuffer *buf,
         virBufferAsprintf(&targetAttrBuf, " hotplug='%s'",
                           virTristateSwitchTypeToString(def->opts.pciopts.hotplug));
     }
+    if (def->opts.pciopts.memReserve) {
+        virBufferAsprintf(&targetAttrBuf, " memReserve='%llu'",
+                          def->opts.pciopts.memReserve);
+    }
 
     if (def->opts.pciopts.numaNode != -1)
         virBufferAsprintf(&targetChildBuf, "<node>%d</node>\n", def->opts.pciopts.numaNode);

src/conf/domain_conf.h

@@ -738,6 +738,9 @@ struct _virDomainPCIControllerOpts {
      */
     int numaNode;
     virTristateSwitch hotplug; /* 'off' to prevent hotplug/unplug, default 'on' */
+
+    unsigned long long memReserve; /* used by pci-bridge and pcie-root-port,
+                                      0 == undef, KiB */
 };
 
 struct _virDomainUSBControllerOpts {

src/conf/schemas/domaincommon.rng

@@ -2897,6 +2897,11 @@
                       <ref name="unsignedInt"/>
                     </element>
                   </optional>
+                  <optional>
+                    <attribute name="memReserve">
+                      <ref name="unsignedLong"/>
+                    </attribute>
+                  </optional>
                 </element>
               </optional>
               <!-- *-root controllers have an optional element "pcihole64"-->

tests/qemuxmlconfdata/q35-usb2.x86_64-latest.xml

@@ -30,7 +30,7 @@
     </controller>
     <controller type='pci' index='2' model='pci-bridge'>
       <model name='pci-bridge'/>
-      <target chassisNr='56'/>
+      <target chassisNr='56' memReserve='8196'/>
       <address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
     </controller>
     <controller type='usb' index='0' model='ich9-ehci1'>

tests/qemuxmlconfdata/q35-usb2.xml

@@ -25,7 +25,7 @@
     </controller>
     <controller type='pci' index='2' model='pci-bridge'>
       <model name='pci-bridge'/>
-      <target chassisNr='56'/>
+      <target chassisNr='56' memReserve='8196'/>
     </controller>
     <controller type='usb' index='0' model='ich9-ehci1'/>
     <controller type='usb' index='0' model='ich9-uhci1'/>