qemuBuildThreadContextProps: Prune .node-affinity wrt <emulatorpin/>

When a thread-context object is specified on the cmd line, then
QEMU spawns a thread and sets its affinity to the list of NUMA
nodes specified in .node-affinity attribute. And this works just
fine, until the main QEMU thread itself is not restricted.

Because of v5.3.0-rc1~18 we restrict the main emulator thread
even before QEMU is executed and thus then it tries to set
affinity of a thread-context thread, it inevitably fails with:

  Setting CPU affinity failed: Invalid argument

Now, we could lift the pinning temporarily, let QEMU spawn all
thread-context threads, and enforce pinning again, but that would
require some form of communication with QEMU (maybe -preconfig?).
But that would still be wrong, because it would circumvent
<emulatorpin/>.

Technically speaking, thread-context is an internal
implementation detail of QEMU, and if it weren't for it, the main
emulator thread would be doing the allocation. Therefore, we
should honor the pinning and prune the list of node so that
inaccessible ones are dropped.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2154750
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Kristina Hanicova <khanicov@redhat.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>

src/qemu/qemu_command.c

@@ -3539,7 +3539,7 @@ qemuBuildMemoryDimmBackendStr(virCommand *cmd,
                                     def, mem, true, false, &nodemask) < 0)
         return -1;
 
-    if (qemuBuildThreadContextProps(&tcProps, &props, priv, nodemask) < 0)
+    if (qemuBuildThreadContextProps(&tcProps, &props, def, priv, nodemask) < 0)
         return -1;
 
     if (tcProps &&
@@ -3636,10 +3636,13 @@ qemuBuildMemoryDeviceProps(virQEMUDriverConfig *cfg,
 int
 qemuBuildThreadContextProps(virJSONValue **tcProps,
                             virJSONValue **memProps,
+                            const virDomainDef *def,
                             qemuDomainObjPrivate *priv,
                             virBitmap *nodemask)
 {
     g_autoptr(virJSONValue) props = NULL;
+    virBitmap *emulatorpin = NULL;
+    g_autoptr(virBitmap) emulatorNodes = NULL;
     g_autofree char *tcAlias = NULL;
     const char *memalias = NULL;
     bool prealloc = false;
@@ -3656,6 +3659,22 @@ qemuBuildThreadContextProps(virJSONValue **tcProps,
         !prealloc)
         return 0;
 
+    emulatorpin = qemuDomainEvaluateCPUMask(def,
+                                            def->cputune.emulatorpin,
+                                            priv->autoNodeset);
+
+    if (emulatorpin && virNumaIsAvailable()) {
+        if (virNumaCPUSetToNodeset(emulatorpin, &emulatorNodes) < 0)
+            return -1;
+
+        virBitmapIntersect(emulatorNodes, nodemask);
+
+        if (virBitmapIsAllClear(emulatorNodes))
+            return 0;
+
+        nodemask = emulatorNodes;
+    }
+
     memalias = virJSONValueObjectGetString(*memProps, "id");
     if (!memalias) {
         virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
@@ -7188,7 +7207,7 @@ qemuBuildMemCommandLineMemoryDefaultBackend(virCommand *cmd,
                                     def, &mem, false, true, &nodemask) < 0)
         return -1;
 
-    if (qemuBuildThreadContextProps(&tcProps, &props, priv, nodemask) < 0)
+    if (qemuBuildThreadContextProps(&tcProps, &props, def, priv, nodemask) < 0)
         return -1;
 
     if (tcProps &&
@@ -7517,7 +7536,7 @@ qemuBuildNumaCommandLine(virQEMUDriverConfig *cfg,
             g_autoptr(virJSONValue) tcProps = NULL;
 
             if (qemuBuildThreadContextProps(&tcProps, &nodeBackends[i],
-                                            priv, nodemask[i]) < 0)
+                                            def, priv, nodemask[i]) < 0)
                 goto cleanup;
 
             if (tcProps &&

src/qemu/qemu_command.h

@@ -153,6 +153,7 @@ qemuBuildMemoryDeviceProps(virQEMUDriverConfig *cfg,
 int
 qemuBuildThreadContextProps(virJSONValue **tcProps,
                             virJSONValue **memProps,
+                            const virDomainDef *def,
                             qemuDomainObjPrivate *priv,
                             virBitmap *nodemask);
 

tests/qemuxml2argvdata/memory-hotplug-dimm-addr.x86_64-latest.args

@@ -28,7 +28,7 @@ XDG_CONFIG_HOME=/var/lib/libvirt/qemu/domain--1-QEMUGuest1/.config \
 -no-shutdown \
 -boot strict=on \
 -device '{"driver":"piix3-usb-uhci","id":"usb","bus":"pci.0","addr":"0x1.0x2"}' \
--object '{"qom-type":"thread-context","id":"tc-memdimm0","node-affinity":[1,2,3]}' \
+-object '{"qom-type":"thread-context","id":"tc-memdimm0","node-affinity":[1,2]}' \
 -object '{"qom-type":"memory-backend-file","id":"memdimm0","mem-path":"/dev/hugepages2M/libvirt/qemu/-1-QEMUGuest1","prealloc":true,"size":536870912,"host-nodes":[1,2,3],"policy":"bind","prealloc-context":"tc-memdimm0"}' \
 -device '{"driver":"pc-dimm","node":0,"memdev":"memdimm0","id":"dimm0","slot":0,"addr":4294967296}' \
 -object '{"qom-type":"memory-backend-ram","id":"memdimm2","size":536870912}' \