qemu: Don't generate '-machine memory-backend' and '-numa memdev'

In 88957116c9 I've switched to -machine memory-backend=ID and
-object memory-backend-* because QEMU is obsoleting -mem-path
and -mem-prealloc. However, what I did not foresee was that using
-machine memory-backend in combination with -numa is not allowed
in QEMU. This was reported upstream and fortunately not released
yet.

The problem is that if domain has NUMA nodes then we will
generate memory-backend-* objects for NUMA nodes (because if QEMU
is new enough to expose default RAM ID it also supports -numa
memdev=) and adding non-NUMA memory backend is wrong.

Reported-by: Masayoshi Mizuma <msys.mizuma@gmail.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>

src/qemu/qemu_command.c

@@ -6829,7 +6829,6 @@ qemuBuildMachineCommandLine(virCommandPtr cmd,
     virTristateSwitch vmport = def->features[VIR_DOMAIN_FEATURE_VMPORT];
     virTristateSwitch smm = def->features[VIR_DOMAIN_FEATURE_SMM];
     virCPUDefPtr cpu = def->cpu;
-    const char *defaultRAMid = NULL;
     g_auto(virBuffer) buf = VIR_BUFFER_INITIALIZER;
     size_t i;
 
@@ -7046,11 +7045,24 @@ qemuBuildMachineCommandLine(virCommandPtr cmd,
     if (virDomainNumaHasHMAT(def->numa))
         virBufferAddLit(&buf, ",hmat=on");
 
-    defaultRAMid = virQEMUCapsGetMachineDefaultRAMid(qemuCaps,
+    if (!virDomainNumaGetNodeCount(def->numa)) {
-                                                     def->virtType,
+        const char *defaultRAMid = NULL;
-                                                     def->os.machine);
+
-    if (defaultRAMid)
+        /* QEMU is obsoleting -mem-path and -mem-prealloc. That means we have
-        virBufferAsprintf(&buf, ",memory-backend=%s", defaultRAMid);
+         * to switch to memory-backend-* even for regular RAM and to keep
+         * domain migratable we have to set the same ID as older QEMUs would.
+         * If domain has no NUMA nodes and QEMU is new enough to expose ID of
+         * the default RAM we want to use it for default RAM (construct
+         * memory-backend-* with corresponding attributes instead of obsolete
+         * -mem-path and -mem-prealloc).
+         * This generates only reference for the memory-backend-* object added
+         * later in qemuBuildMemCommandLine() */
+        defaultRAMid = virQEMUCapsGetMachineDefaultRAMid(qemuCaps,
+                                                         def->virtType,
+                                                         def->os.machine);
+        if (defaultRAMid)
+            virBufferAsprintf(&buf, ",memory-backend=%s", defaultRAMid);
+    }
 
     virCommandAddArgBuffer(cmd, &buf);
 
@@ -7216,7 +7228,13 @@ qemuBuildMemCommandLine(virCommandPtr cmd,
                                                      def->os.machine);
 
     if (defaultRAMid) {
-        qemuBuildMemCommandLineMemoryDefaultBackend(cmd, def, priv, defaultRAMid);
+        /* As documented in qemuBuildMachineCommandLine() if QEMU is new enough
+         * to expose default RAM ID we must use memory-backend-* even for
+         * regular memory because -mem-path and -mem-prealloc are obsolete.
+         * However, if domain has one or more NUMA nodes then there is no
+         * default RAM and we mustn't generate the memory object. */
+        if (!virDomainNumaGetNodeCount(def->numa))
+            qemuBuildMemCommandLineMemoryDefaultBackend(cmd, def, priv, defaultRAMid);
     } else {
         if (def->mem.allocation == VIR_DOMAIN_MEMORY_ALLOCATION_IMMEDIATE) {
             virCommandAddArgList(cmd, "-mem-prealloc", NULL);

tests/qemuxml2argvdata/hugepages-nvdimm.x86_64-latest.args

@@ -12,13 +12,9 @@ QEMU_AUDIO_DRV=none \
 -S \
 -object secret,id=masterKey0,format=raw,\
 file=/tmp/lib/domain--1-QEMUGuest1/master-key.aes \
--machine pc,accel=tcg,usb=off,dump-guest-core=off,nvdimm=on,\
+-machine pc,accel=tcg,usb=off,dump-guest-core=off,nvdimm=on \
-memory-backend=pc.ram \
 -cpu qemu64 \
 -m size=1048576k,slots=16,maxmem=1099511627776k \
--object memory-backend-file,id=pc.ram,\
-mem-path=/dev/hugepages2M/libvirt/qemu/-1-QEMUGuest1,share=yes,prealloc=yes,\
-size=1073741824 \
 -overcommit mem-lock=off \
 -smp 2,sockets=2,dies=1,cores=1,threads=1 \
 -object memory-backend-file,id=ram-node0,\

tests/qemuxml2argvdata/memfd-memory-default-hugepage.x86_64-latest.args

@@ -12,12 +12,9 @@ QEMU_AUDIO_DRV=none \
 -S \
 -object secret,id=masterKey0,format=raw,\
 file=/tmp/lib/domain--1-instance-00000092/master-key.aes \
--machine pc-i440fx-2.3,accel=kvm,usb=off,dump-guest-core=off,\
+-machine pc-i440fx-2.3,accel=kvm,usb=off,dump-guest-core=off \
-memory-backend=pc.ram \
 -cpu qemu64 \
 -m 14336 \
--object memory-backend-memfd,id=pc.ram,hugetlb=yes,hugetlbsize=2097152,\
-share=yes,prealloc=yes,size=15032385536 \
 -overcommit mem-lock=off \
 -smp 8,sockets=1,dies=1,cores=8,threads=1 \
 -object memory-backend-memfd,id=ram-node0,hugetlb=yes,hugetlbsize=2097152,\

tests/qemuxml2argvdata/memfd-memory-numa.x86_64-latest.args

@@ -12,12 +12,9 @@ QEMU_AUDIO_DRV=none \
 -S \
 -object secret,id=masterKey0,format=raw,\
 file=/tmp/lib/domain--1-instance-00000092/master-key.aes \
--machine pc-i440fx-2.3,accel=kvm,usb=off,dump-guest-core=off,\
+-machine pc-i440fx-2.3,accel=kvm,usb=off,dump-guest-core=off \
-memory-backend=pc.ram \
 -cpu qemu64 \
 -m 14336 \
--object memory-backend-memfd,id=pc.ram,hugetlb=yes,hugetlbsize=2097152,\
-share=yes,prealloc=yes,size=15032385536 \
 -overcommit mem-lock=off \
 -smp 8,sockets=1,dies=1,cores=8,threads=1 \
 -object memory-backend-memfd,id=ram-node0,hugetlb=yes,hugetlbsize=2097152,\

tests/qemuxml2argvdata/memory-hotplug-nvdimm-access.x86_64-latest.args

@@ -12,11 +12,9 @@ QEMU_AUDIO_DRV=none \
 -S \
 -object secret,id=masterKey0,format=raw,\
 file=/tmp/lib/domain--1-QEMUGuest1/master-key.aes \
--machine pc,accel=tcg,usb=off,dump-guest-core=off,nvdimm=on,\
+-machine pc,accel=tcg,usb=off,dump-guest-core=off,nvdimm=on \
-memory-backend=pc.ram \
 -cpu qemu64 \
 -m size=219136k,slots=16,maxmem=1099511627776k \
--object memory-backend-ram,id=pc.ram,size=224395264 \
 -overcommit mem-lock=off \
 -smp 2,sockets=2,dies=1,cores=1,threads=1 \
 -object memory-backend-ram,id=ram-node0,size=224395264 \

tests/qemuxml2argvdata/memory-hotplug-nvdimm-align.x86_64-latest.args

@@ -12,11 +12,9 @@ QEMU_AUDIO_DRV=none \
 -S \
 -object secret,id=masterKey0,format=raw,\
 file=/tmp/lib/domain--1-QEMUGuest1/master-key.aes \
--machine pc,accel=tcg,usb=off,dump-guest-core=off,nvdimm=on,\
+-machine pc,accel=tcg,usb=off,dump-guest-core=off,nvdimm=on \
-memory-backend=pc.ram \
 -cpu qemu64 \
 -m size=219136k,slots=16,maxmem=1099511627776k \
--object memory-backend-ram,id=pc.ram,size=224395264 \
 -overcommit mem-lock=off \
 -smp 2,sockets=2,dies=1,cores=1,threads=1 \
 -object memory-backend-ram,id=ram-node0,size=224395264 \

tests/qemuxml2argvdata/memory-hotplug-nvdimm-label.x86_64-latest.args

@@ -12,11 +12,9 @@ QEMU_AUDIO_DRV=none \
 -S \
 -object secret,id=masterKey0,format=raw,\
 file=/tmp/lib/domain--1-QEMUGuest1/master-key.aes \
--machine pc,accel=tcg,usb=off,dump-guest-core=off,nvdimm=on,\
+-machine pc,accel=tcg,usb=off,dump-guest-core=off,nvdimm=on \
-memory-backend=pc.ram \
 -cpu qemu64 \
 -m size=219136k,slots=16,maxmem=1099511627776k \
--object memory-backend-ram,id=pc.ram,size=224395264 \
 -overcommit mem-lock=off \
 -smp 2,sockets=2,dies=1,cores=1,threads=1 \
 -object memory-backend-ram,id=ram-node0,size=224395264 \

tests/qemuxml2argvdata/memory-hotplug-nvdimm-pmem.x86_64-latest.args

@@ -12,11 +12,9 @@ QEMU_AUDIO_DRV=none \
 -S \
 -object secret,id=masterKey0,format=raw,\
 file=/tmp/lib/domain--1-QEMUGuest1/master-key.aes \
--machine pc,accel=tcg,usb=off,dump-guest-core=off,nvdimm=on,\
+-machine pc,accel=tcg,usb=off,dump-guest-core=off,nvdimm=on \
-memory-backend=pc.ram \
 -cpu qemu64 \
 -m size=219136k,slots=16,maxmem=1099511627776k \
--object memory-backend-ram,id=pc.ram,size=224395264 \
 -overcommit mem-lock=off \
 -smp 2,sockets=2,dies=1,cores=1,threads=1 \
 -object memory-backend-ram,id=ram-node0,size=224395264 \

tests/qemuxml2argvdata/memory-hotplug-nvdimm-readonly.x86_64-latest.args

@@ -12,11 +12,9 @@ QEMU_AUDIO_DRV=none \
 -S \
 -object secret,id=masterKey0,format=raw,\
 file=/tmp/lib/domain--1-QEMUGuest1/master-key.aes \
--machine pc,accel=tcg,usb=off,dump-guest-core=off,nvdimm=on,\
+-machine pc,accel=tcg,usb=off,dump-guest-core=off,nvdimm=on \
-memory-backend=pc.ram \
 -cpu qemu64 \
 -m size=219136k,slots=16,maxmem=1099511627776k \
--object memory-backend-ram,id=pc.ram,size=224395264 \
 -overcommit mem-lock=off \
 -smp 2,sockets=2,dies=1,cores=1,threads=1 \
 -object memory-backend-ram,id=ram-node0,size=224395264 \

tests/qemuxml2argvdata/memory-hotplug-nvdimm.x86_64-latest.args

@@ -12,11 +12,9 @@ QEMU_AUDIO_DRV=none \
 -S \
 -object secret,id=masterKey0,format=raw,\
 file=/tmp/lib/domain--1-QEMUGuest1/master-key.aes \
--machine pc,accel=tcg,usb=off,dump-guest-core=off,nvdimm=on,\
+-machine pc,accel=tcg,usb=off,dump-guest-core=off,nvdimm=on \
-memory-backend=pc.ram \
 -cpu qemu64 \
 -m size=1048576k,slots=16,maxmem=1099511627776k \
--object memory-backend-ram,id=pc.ram,size=1073741824 \
 -overcommit mem-lock=off \
 -smp 2,sockets=2,dies=1,cores=1,threads=1 \
 -object memory-backend-ram,id=ram-node0,size=1073741824 \

tests/qemuxml2argvdata/numatune-hmat.x86_64-latest.args

@@ -12,11 +12,9 @@ QEMU_AUDIO_DRV=none \
 -S \
 -object secret,id=masterKey0,format=raw,\
 file=/tmp/lib/domain--1-QEMUGuest/master-key.aes \
--machine pc,accel=tcg,usb=off,dump-guest-core=off,hmat=on,\
+-machine pc,accel=tcg,usb=off,dump-guest-core=off,hmat=on \
-memory-backend=pc.ram \
 -cpu qemu64 \
 -m 12288 \
--object memory-backend-ram,id=pc.ram,size=12884901888 \
 -overcommit mem-lock=off \
 -smp 12,sockets=12,cores=1,threads=1 \
 -object memory-backend-ram,id=ram-node0,size=2147483648 \

tests/qemuxml2argvdata/vhost-user-fs-fd-memory.x86_64-latest.args

@@ -12,11 +12,9 @@ QEMU_AUDIO_DRV=none \
 -S \
 -object secret,id=masterKey0,format=raw,\
 file=/tmp/lib/domain--1-guest/master-key.aes \
--machine pc,accel=kvm,usb=off,dump-guest-core=off,memory-backend=pc.ram \
+-machine pc,accel=kvm,usb=off,dump-guest-core=off \
 -cpu qemu64 \
 -m 14336 \
--object memory-backend-file,id=pc.ram,\
-mem-path=/var/lib/libvirt/qemu/ram/-1-guest/pc.ram,share=yes,size=15032385536 \
 -overcommit mem-lock=off \
 -smp 2,sockets=2,cores=1,threads=1 \
 -object memory-backend-file,id=ram-node0,\

tests/qemuxml2argvdata/vhost-user-fs-hugepages.x86_64-latest.args

@@ -12,12 +12,9 @@ QEMU_AUDIO_DRV=none \
 -S \
 -object secret,id=masterKey0,format=raw,\
 file=/tmp/lib/domain--1-guest/master-key.aes \
--machine q35,accel=tcg,usb=off,dump-guest-core=off,memory-backend=pc.ram \
+-machine q35,accel=tcg,usb=off,dump-guest-core=off \
 -cpu qemu64 \
 -m 2048 \
--object memory-backend-file,id=pc.ram,\
-mem-path=/dev/hugepages2M/libvirt/qemu/-1-guest,share=yes,prealloc=yes,\
-size=2147483648 \
 -overcommit mem-lock=off \
 -smp 2,sockets=2,cores=1,threads=1 \
 -object memory-backend-file,id=ram-node0,\

tests/qemuxml2argvdata/vhost-user-gpu-secondary.x86_64-latest.args

@@ -12,10 +12,9 @@ QEMU_AUDIO_DRV=none \
 -S \
 -object secret,id=masterKey0,format=raw,\
 file=/tmp/lib/domain--1-QEMUGuest1/master-key.aes \
--machine pc,accel=tcg,usb=off,dump-guest-core=off,memory-backend=pc.ram \
+-machine pc,accel=tcg,usb=off,dump-guest-core=off \
 -cpu qemu64 \
 -m 214 \
--object memory-backend-memfd,id=pc.ram,share=yes,size=224395264 \
 -overcommit mem-lock=off \
 -smp 1,sockets=1,cores=1,threads=1 \
 -object memory-backend-memfd,id=ram-node0,share=yes,size=224395264 \

tests/qemuxml2argvdata/vhost-user-vga.x86_64-latest.args

@@ -12,10 +12,9 @@ QEMU_AUDIO_DRV=none \
 -S \
 -object secret,id=masterKey0,format=raw,\
 file=/tmp/lib/domain--1-QEMUGuest1/master-key.aes \
--machine pc,accel=tcg,usb=off,dump-guest-core=off,memory-backend=pc.ram \
+-machine pc,accel=tcg,usb=off,dump-guest-core=off \
 -cpu qemu64 \
 -m 214 \
--object memory-backend-memfd,id=pc.ram,share=yes,size=224395264 \
 -overcommit mem-lock=off \
 -smp 1,sockets=1,cores=1,threads=1 \
 -object memory-backend-memfd,id=ram-node0,share=yes,size=224395264 \