[libvirt] [PATCH 4/4] qemu: Fix qemuProcessInitCpuAffinity()

[Andrea Bolognani]

Commit f136b83139c6 made some changes in the way we set CPU
affinity for QEMU processes, and while doing so unfortunately
also introduced a logic bug in that it tried to use a NUMA node
map where a CPU map was expected.

Because of that, guests using <numatune> would suddenly fail to
start:

  # virsh start guest
  error: Failed to start domain guest
  error: cannot set CPU affinity on process 40055: Invalid argument

This was particularly easy to trigger on POWER 8 machines,
where secondary threads always show up as offline in the host:
having

  <numatune>
    <memory mode='strict' placement='static' nodeset='1'/>
  </numatune>

in the guest configuration, for example, would result in libvirt
trying to set the process affinity so that it would prefer
running on CPU 1, but since that's a secondary thread and thus
shows up as offline, the operation would fail, and so would
starting the guest.

Use the newly introduced virNumaNodesetToCPUset() to convert
the NUMA node map to a CPU map, which in the example above would
be 8-15 with CPU 8 showing up as online in the guest.

https://bugzilla.redhat.com/show_bug.cgi?id=1703661

Signed-off-by: Andrea Bolognani <abologna at redhat.com>
---
 src/qemu/qemu_process.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index fa5909e9be..295ad2e1ff 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -2489,11 +2489,16 @@ qemuProcessInitCpuAffinity(virDomainObjPtr vm)
     if (virDomainNumaGetNodeCount(vm->def->numa) <= 1 &&
         virDomainNumatuneGetMode(vm->def->numa, -1, &mem_mode) == 0 &&
         mem_mode == VIR_DOMAIN_NUMATUNE_MEM_STRICT) {
+        virBitmapPtr nodeset = NULL;
+
         if (virDomainNumatuneMaybeGetNodeset(vm->def->numa,
                                              priv->autoNodeset,
-                                             &cpumapToSet,
+                                             &nodeset,
                                              -1) < 0)
             goto cleanup;
+
+        if (virNumaNodesetToCPUset(nodeset, &cpumapToSet) < 0)
+            goto cleanup;
     } else if (vm->def->cputune.emulatorpin) {
         cpumapToSet = vm->def->cputune.emulatorpin;
     } else {
-- 
2.21.0