When we are about to spawn QEMU, we validate the domain definition against qemuCaps. Except when domain is/was already running before (i.e. on incoming migration, snapshots, resume from a file). However, especially on incoming migration it may happen that the destination QEMU is different to the source QEMU, e.g. the destination QEMU may have some devices disabled. And we have a function that validates devices/features requested in domain XML against the desired QEMU capabilities (aka qemuCaps) - it's virDomainDefValidate() which calls qemuValidateDomainDef() and qemuValidateDomainDeviceDef() subsequently. But the problem here is that the validation function is explicitly skipped over in specific scenarios (like incoming migration, restore from a snapshot or previously saved file). This in turn means that we may spawn QEMU and request device/features it doesn't support. When that happens QEMU fails to load migration stream: qemu-kvm: ... 'virtio-mem-pci' is not a valid device model name (NB, while the example shows one particular device, the problem is paramount) This problem is easier to run into since we are slowly moving validation from qemu_command.c into said validation functions. The solution is simple: do the validation in all cases. And while it may happen that users would be unable to migrate/restore a guest due to a bug in our validator, spawning QEMU without validation is worse (especially when you consider that users can supply their own XMLs for migrate/restore operations - these were never validated). Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2048435 Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com&gt; --- Technically, this is v2 of: https://listman.redhat.com/archives/libvir-list/2022-January/msg01307.html but since it implements completely different approach I've reset the counter. src/qemu/qemu_process.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c index c13280c8f3..ea586e54c1 100644 --- a/src/qemu/qemu_process.c +++ b/src/qemu/qemu_process.c @@ -5399,11 +5399,7 @@ qemuProcessStartValidate(virQEMUDriver *driver, } - /* Checks below should not be executed when starting a qemu process for a - * VM that was running before (migration, snapshots, save). It's more - * important to start such VM than keep the configuration clean */ - if ((flags & VIR_QEMU_PROCESS_START_NEW) && - virDomainDefValidate(vm->def, 0, driver->xmlopt, qemuCaps) < 0) + if (virDomainDefValidate(vm->def, 0, driver->xmlopt, qemuCaps) < 0) return -1; if (qemuProcessStartValidateGraphics(vm) < 0) -- 2.34.1