qemu: Relax validation for mem->access if guest has no NUMA

In v6.8.0-27-g88957116c9 and friends I've switched the way the
default RAM is specified for QEMU (from plain -m to
memory-backend-*). This means, that even if a guest doesn't have
any NUMA nodes configured we can use memory-backend-* attributes
to translate user config requests. For instance, we can allow
memory to be shared (<access mode='shared'/> under
<memoryBacking/>). But what my original commits are missing is
allowing such configuration in our validator.

Fixes: 88957116c9
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1839034#c12
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

src/qemu/qemu_validate.c

@@ -754,6 +754,9 @@ static int
 qemuValidateDomainDefMemory(const virDomainDef *def,
                             virQEMUCapsPtr qemuCaps)
 {
+    const char *defaultRAMid = virQEMUCapsGetMachineDefaultRAMid(qemuCaps,
+                                                                 def->virtType,
+                                                                 def->os.machine);
     const long system_page_size = virGetSystemPageSizeKB();
     const virDomainMemtune *mem = &def->mem;
 
@@ -781,9 +784,10 @@ qemuValidateDomainDefMemory(const virDomainDef *def,
         return -1;
     }
 
-    /* We can't guarantee any other mem.access
+    /* We can't guarantee any other mem.access if no guest NUMA
-     * if no guest NUMA nodes are defined. */
+     * nodes are defined, unless defaultRAMid is provided. */
-    if (mem->hugepages[0].size != system_page_size &&
+    if (!defaultRAMid &&
+        mem->hugepages[0].size != system_page_size &&
         virDomainNumaGetNodeCount(def->numa) == 0 &&
         mem->access != VIR_DOMAIN_MEMORY_ACCESS_DEFAULT &&
         mem->access != VIR_DOMAIN_MEMORY_ACCESS_PRIVATE) {

tests/qemuxml2argvdata/hugepages-memaccess3.x86_64-latest.args

@@ -0,0 +1,39 @@
+LC_ALL=C \
+PATH=/bin \
+HOME=/tmp/lib/domain--1-fedora \
+USER=test \
+LOGNAME=test \
+XDG_DATA_HOME=/tmp/lib/domain--1-fedora/.local/share \
+XDG_CACHE_HOME=/tmp/lib/domain--1-fedora/.cache \
+XDG_CONFIG_HOME=/tmp/lib/domain--1-fedora/.config \
+QEMU_AUDIO_DRV=none \
+/usr/bin/qemu-system-x86_64 \
+-name guest=fedora,debug-threads=on \
+-S \
+-object secret,id=masterKey0,format=raw,\
+file=/tmp/lib/domain--1-fedora/master-key.aes \
+-machine pc-i440fx-2.9,accel=kvm,usb=off,dump-guest-core=off,\
+memory-backend=pc.ram \
+-cpu EPYC-Rome,x2apic=on,tsc-deadline=on,hypervisor=on,tsc-adjust=on,stibp=on,\
+arch-capabilities=on,ssbd=on,xsaves=on,cmp-legacy=on,amd-ssbd=on,virt-ssbd=on,\
+rdctl-no=on,skip-l1dfl-vmentry=on,mds-no=on,pschange-mc-no=on \
+-m 4096 \
+-object memory-backend-file,id=pc.ram,\
+mem-path=/dev/hugepages2M/libvirt/qemu/-1-fedora,share=yes,prealloc=yes,\
+size=4294967296 \
+-overcommit mem-lock=off \
+-smp 4,sockets=4,cores=1,threads=1 \
+-uuid 63840878-0deb-4095-97e6-fc444d9bc9fa \
+-display none \
+-no-user-config \
+-nodefaults \
+-chardev socket,id=charmonitor,fd=1729,server,nowait \
+-mon chardev=charmonitor,id=monitor,mode=control \
+-rtc base=utc \
+-no-shutdown \
+-no-acpi \
+-boot menu=on,strict=on \
+-device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 \
+-sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,\
+resourcecontrol=deny \
+-msg timestamp=on

tests/qemuxml2argvtest.c

@@ -1145,6 +1145,7 @@ mymain(void)
     DO_TEST_PARSE_ERROR("hugepages-memaccess3",
                         QEMU_CAPS_OBJECT_MEMORY_RAM,
                         QEMU_CAPS_OBJECT_MEMORY_FILE);
+    DO_TEST_CAPS_LATEST("hugepages-memaccess3");
     DO_TEST_CAPS_LATEST("hugepages-nvdimm");
     DO_TEST("nosharepages", QEMU_CAPS_MEM_MERGE);
     DO_TEST("disk-cdrom", NONE);