https://bugzilla.redhat.com/show_bug.cgi?id=1458638

This code is so complicated because we allow enabling the same
bits at many places. Just like in this case: huge pages can be
enabled by global <hugepages/> element under <memoryBacking> or
on per <memory/> basis. To complicate things a bit more, users
are allowed to not specify any specific page size in which case
the default page size is used. And this is what is causing this
bug. If no page size is specified, @pagesize is keeping value of
zero throughout whole function. Therefore we need yet another
boolean to hold [use, don't use] information as we can't sue
@pagesize for that.

Signed-off-by: Michal Privoznik <mpriv...@redhat.com>
---
 src/qemu/qemu_command.c                            | 22 ++++++--
 .../qemuxml2argv-hugepages-pages7.args             | 35 ++++++++++++
 .../qemuxml2argv-hugepages-pages7.xml              | 65 ++++++++++++++++++++++
 tests/qemuxml2argvtest.c                           |  2 +
 .../qemuxml2xmlout-hugepages-pages7.xml            |  1 +
 tests/qemuxml2xmltest.c                            |  1 +
 6 files changed, 120 insertions(+), 6 deletions(-)
 create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-hugepages-pages7.args
 create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-hugepages-pages7.xml
 create mode 120000 tests/qemuxml2xmloutdata/qemuxml2xmlout-hugepages-pages7.xml

diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 604650596..68fc13706 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -3250,8 +3250,6 @@ qemuBuildMemoryBackendStr(virJSONValuePtr *backendProps,
                           virBitmapPtr autoNodeset,
                           bool force)
 {
-    virDomainHugePagePtr master_hugepage = NULL;
-    virDomainHugePagePtr hugepage = NULL;
     virDomainNumatuneMemMode mode;
     const long system_page_size = virGetSystemPageSizeKB();
     virDomainMemoryAccess memAccess = mem->access;
@@ -3264,6 +3262,13 @@ qemuBuildMemoryBackendStr(virJSONValuePtr *backendProps,
     bool nodeSpecified = virDomainNumatuneNodeSpecified(def->numa, 
mem->targetNode);
     unsigned long long pagesize = mem->pagesize;
     bool needHugepage = !!pagesize;
+    bool useHugepage = !!pagesize;
+
+    /* The difference between @needHugepage and @useHugepage is that the latter
+     * is true whenever huge page is defined for the current memory cell.
+     * Either directly, or transitively via global domain huge pages. The
+     * former is true whenever "memory-backend-file" must be used to satisfy
+     * @useHugepage. */
 
     *backendProps = NULL;
     *backendType = NULL;
@@ -3290,6 +3295,8 @@ qemuBuildMemoryBackendStr(virJSONValuePtr *backendProps,
         mode = VIR_DOMAIN_NUMATUNE_MEM_STRICT;
 
     if (pagesize == 0) {
+        virDomainHugePagePtr master_hugepage = NULL;
+        virDomainHugePagePtr hugepage = NULL;
         bool thisHugepage = false;
 
         /* Find the huge page size we want to use */
@@ -3327,8 +3334,10 @@ qemuBuildMemoryBackendStr(virJSONValuePtr *backendProps,
             hugepage = master_hugepage;
         }
 
-        if (hugepage)
+        if (hugepage) {
             pagesize = hugepage->size;
+            useHugepage = true;
+        }
     }
 
     if (pagesize == system_page_size) {
@@ -3336,17 +3345,18 @@ qemuBuildMemoryBackendStr(virJSONValuePtr *backendProps,
          * of regular system page size, it's as if they
          * hasn't specified any huge pages at all. */
         pagesize = 0;
-        hugepage = NULL;
+        needHugepage = false;
+        useHugepage = false;
     }
 
     if (!(props = virJSONValueNewObject()))
         return -1;
 
-    if (pagesize || mem->nvdimmPath || memAccess ||
+    if (useHugepage || mem->nvdimmPath || memAccess ||
         def->mem.source == VIR_DOMAIN_MEMORY_SOURCE_FILE) {
         *backendType = "memory-backend-file";
 
-        if (pagesize) {
+        if (useHugepage) {
             if (qemuGetDomainHupageMemPath(def, cfg, pagesize, &memPath) < 0)
                 goto cleanup;
             prealloc = true;
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-hugepages-pages7.args 
b/tests/qemuxml2argvdata/qemuxml2argv-hugepages-pages7.args
new file mode 100644
index 000000000..e4229dce6
--- /dev/null
+++ b/tests/qemuxml2argvdata/qemuxml2argv-hugepages-pages7.args
@@ -0,0 +1,35 @@
+LC_ALL=C \
+PATH=/bin \
+HOME=/home/test \
+USER=test \
+LOGNAME=test \
+QEMU_AUDIO_DRV=none \
+/usr/bin/qemu-system-x86_64 \
+-name fedora \
+-S \
+-M pc-i440fx-2.3 \
+-m size=1048576k,slots=16,maxmem=1099511627776k \
+-smp 2,sockets=2,cores=1,threads=1 \
+-mem-prealloc \
+-mem-path /dev/hugepages2M/libvirt/qemu/-1-fedora \
+-numa node,nodeid=0,cpus=0-1,mem=1024 \
+-object memory-backend-file,id=memdimm0,prealloc=yes,\
+mem-path=/dev/hugepages1G/libvirt/qemu/-1-fedora,size=1073741824,\
+host-nodes=1-3,policy=bind \
+-device pc-dimm,node=0,memdev=memdimm0,id=dimm0,slot=0 \
+-object memory-backend-file,id=memdimm1,prealloc=yes,\
+mem-path=/dev/hugepages2M/libvirt/qemu/-1-fedora,share=no,size=536870912 \
+-device pc-dimm,node=0,memdev=memdimm1,id=dimm1,slot=1 \
+-uuid 63840878-0deb-4095-97e6-fc444d9bc9fa \
+-nographic \
+-nodefaults \
+-chardev socket,id=charmonitor,path=/tmp/lib/domain--1-fedora/monitor.sock,\
+server,nowait \
+-mon chardev=charmonitor,id=monitor,mode=readline \
+-boot c \
+-usb \
+-drive file=/var/lib/libvirt/images/fedora.qcow2,format=qcow2,if=none,\
+id=drive-virtio-disk0 \
+-device virtio-blk-pci,bus=pci.0,addr=0x7,drive=drive-virtio-disk0,\
+id=virtio-disk0 \
+-device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-hugepages-pages7.xml 
b/tests/qemuxml2argvdata/qemuxml2argv-hugepages-pages7.xml
new file mode 100644
index 000000000..d75cf5afa
--- /dev/null
+++ b/tests/qemuxml2argvdata/qemuxml2argv-hugepages-pages7.xml
@@ -0,0 +1,65 @@
+<domain type='qemu'>
+  <name>fedora</name>
+  <uuid>63840878-0deb-4095-97e6-fc444d9bc9fa</uuid>
+  <maxMemory slots='16' unit='KiB'>1099511627776</maxMemory>
+  <memory unit='KiB'>2621439</memory>
+  <currentMemory unit='KiB'>2621439</currentMemory>
+  <memoryBacking>
+    <hugepages/>
+  </memoryBacking>
+  <vcpu placement='static'>2</vcpu>
+  <os>
+    <type arch='x86_64' machine='pc-i440fx-2.3'>hvm</type>
+    <boot dev='hd'/>
+  </os>
+  <features>
+    <acpi/>
+    <apic/>
+    <pae/>
+  </features>
+  <cpu>
+    <numa>
+      <cell id='0' cpus='0-1' memory='1048576' unit='KiB'/>
+    </numa>
+  </cpu>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>restart</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu-system-x86_64</emulator>
+    <disk type='file' device='disk'>
+      <driver name='qemu' type='qcow2'/>
+      <source file='/var/lib/libvirt/images/fedora.qcow2'/>
+      <target dev='vda' bus='virtio'/>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' 
function='0x0'/>
+    </disk>
+    <controller type='usb' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' 
function='0x2'/>
+    </controller>
+    <controller type='pci' index='0' model='pci-root'/>
+    <input type='mouse' bus='ps2'/>
+    <input type='keyboard' bus='ps2'/>
+    <memballoon model='virtio'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' 
function='0x0'/>
+    </memballoon>
+    <memory model='dimm'>
+      <source>
+        <nodemask>1-3</nodemask>
+        <pagesize unit='KiB'>1048576</pagesize>
+      </source>
+      <target>
+        <size unit='KiB'>1048576</size>
+        <node>0</node>
+      </target>
+      <address type='dimm' slot='0'/>
+    </memory>
+    <memory model='dimm' access='private'>
+      <target>
+        <size unit='KiB'>524287</size>
+        <node>0</node>
+      </target>
+      <address type='dimm' slot='1'/>
+    </memory>
+  </devices>
+</domain>
diff --git a/tests/qemuxml2argvtest.c b/tests/qemuxml2argvtest.c
index 655c89bc3..993805231 100644
--- a/tests/qemuxml2argvtest.c
+++ b/tests/qemuxml2argvtest.c
@@ -844,6 +844,8 @@ mymain(void)
             QEMU_CAPS_OBJECT_MEMORY_RAM, QEMU_CAPS_OBJECT_MEMORY_FILE);
     DO_TEST("hugepages-pages5", QEMU_CAPS_MEM_PATH);
     DO_TEST("hugepages-pages6", NONE);
+    DO_TEST("hugepages-pages7", QEMU_CAPS_MEM_PATH,
+            QEMU_CAPS_DEVICE_PC_DIMM, QEMU_CAPS_OBJECT_MEMORY_FILE);
     DO_TEST("hugepages-memaccess", QEMU_CAPS_OBJECT_MEMORY_FILE,
             QEMU_CAPS_OBJECT_MEMORY_RAM, QEMU_CAPS_DEVICE_PC_DIMM,
             QEMU_CAPS_NUMA);
diff --git a/tests/qemuxml2xmloutdata/qemuxml2xmlout-hugepages-pages7.xml 
b/tests/qemuxml2xmloutdata/qemuxml2xmlout-hugepages-pages7.xml
new file mode 120000
index 000000000..9aafa6e95
--- /dev/null
+++ b/tests/qemuxml2xmloutdata/qemuxml2xmlout-hugepages-pages7.xml
@@ -0,0 +1 @@
+../qemuxml2argvdata/qemuxml2argv-hugepages-pages7.xml
\ No newline at end of file
diff --git a/tests/qemuxml2xmltest.c b/tests/qemuxml2xmltest.c
index 0d549adec..311b71356 100644
--- a/tests/qemuxml2xmltest.c
+++ b/tests/qemuxml2xmltest.c
@@ -433,6 +433,7 @@ mymain(void)
     DO_TEST("hugepages-pages4", NONE);
     DO_TEST("hugepages-pages5", NONE);
     DO_TEST("hugepages-pages6", NONE);
+    DO_TEST("hugepages-pages7", NONE);
     DO_TEST("hugepages-shared", NONE);
     DO_TEST("hugepages-memaccess", NONE);
     DO_TEST("hugepages-memaccess2", NONE);
-- 
2.13.0

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