[libvirt] [PATCH] qemu: Forbid <memoryBacking><locked> without <memtune><hard_limit>

[Andrea Bolognani]

In order for memory locking to work, the hard limit on memory
locking (and usage) has to be set appropriately by the user.

The documentation mentions the requirement already: with this
patch, it's going to be enforced by runtime checks as well.

Note that this will make existing guests that don't satisfy
the requirement disappear; that said, such guests have never
been able to start in the first place.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1316774
---
 src/qemu/qemu_domain.c                               | 20 ++++++++++++++++++++
 tests/qemuxml2argvdata/qemuxml2argv-mlock-on.xml     |  3 +++
 ....xml => qemuxml2argv-mlock-without-hardlimit.xml} |  0
 tests/qemuxml2argvtest.c                             |  1 +
 4 files changed, 24 insertions(+)
 copy tests/qemuxml2argvdata/{qemuxml2argv-mlock-on.xml => qemuxml2argv-mlock-without-hardlimit.xml} (100%)

diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index c6ce090..bb29cfe 100644
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -2629,6 +2629,23 @@ qemuDomainDefVcpusPostParse(virDomainDefPtr def)
 
 
 static int
+qemuDomainDefMemoryLockingPostParse(virDomainDefPtr def)
+{
+    /* Memory locking can only work properly if the memory locking limit
+     * for the QEMU process has been raised appropriately: the default one
+     * is extrememly low, so there's no way the guest will fit in there */
+    if (def->mem.locked && !virMemoryLimitIsSet(def->mem.hard_limit)) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                       _("Setting <memoryBacking><locked> requires "
+                         "<memtune><hard_limit> to be set as well"));
+        return -1;
+    }
+
+    return 0;
+}
+
+
+static int
 qemuDomainDefPostParse(virDomainDefPtr def,
                        virCapsPtr caps,
                        unsigned int parseFlags,
@@ -2692,6 +2709,9 @@ qemuDomainDefPostParse(virDomainDefPtr def,
     if (qemuDomainDefVcpusPostParse(def) < 0)
         goto cleanup;
 
+    if (qemuDomainDefMemoryLockingPostParse(def) < 0)
+        goto cleanup;
+
     ret = 0;
  cleanup:
     virObjectUnref(qemuCaps);
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-mlock-on.xml b/tests/qemuxml2argvdata/qemuxml2argv-mlock-on.xml
index 20a5eaa..2046663 100644
--- a/tests/qemuxml2argvdata/qemuxml2argv-mlock-on.xml
+++ b/tests/qemuxml2argvdata/qemuxml2argv-mlock-on.xml
@@ -3,6 +3,9 @@
   <uuid>c7a5fdbd-edaf-9455-926a-d65c16db1809</uuid>
   <memory unit='KiB'>219136</memory>
   <currentMemory unit='KiB'>219136</currentMemory>
+  <memtune>
+    <hard_limit unit='KiB'>256000</hard_limit>
+  </memtune>
   <memoryBacking>
     <locked/>
   </memoryBacking>
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-mlock-on.xml b/tests/qemuxml2argvdata/qemuxml2argv-mlock-without-hardlimit.xml
similarity index 100%
copy from tests/qemuxml2argvdata/qemuxml2argv-mlock-on.xml
copy to tests/qemuxml2argvdata/qemuxml2argv-mlock-without-hardlimit.xml
diff --git a/tests/qemuxml2argvtest.c b/tests/qemuxml2argvtest.c
index 3532cb5..9b2fec5 100644
--- a/tests/qemuxml2argvtest.c
+++ b/tests/qemuxml2argvtest.c
@@ -2129,6 +2129,7 @@ mymain(void)
     DO_TEST_FAILURE("mlock-on", NONE);
     DO_TEST("mlock-off", QEMU_CAPS_REALTIME_MLOCK);
     DO_TEST("mlock-unsupported", NONE);
+    DO_TEST_PARSE_ERROR("mlock-without-hardlimit", NONE);
 
     DO_TEST_PARSE_ERROR("pci-bridge-negative-index-invalid",
                         QEMU_CAPS_DEVICE_PCI_BRIDGE);
-- 
2.7.4