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Commit7aa563630b("pc: Start with modern CPU hotplug interface by default") removed the .needed callback (vmstate_test_use_cpuhp) from vmstate_cpuhp_state in both piix4.c and ich9.c. However, PIIX4 is also used by non-PC boards - MIPS Malta, which does not select CONFIG_ACPI_CPU_HOTPLUG. For MIPS Malta, the linker resolves vmstate_cpu_hotplug to the stub one in acpi-cpu-hotplug-stub.c, which is a zero-initialized VMStateDescription with .fields == NULL. Before commit7aa563630b, .needed() of PIIX4's vmstate_cpuhp_state returned false for MIPS Malta since PIIX4PMState always initialized the field cpu_hotplug_legacy as true. Malta implicitly relies on this initial value to bypass vmstate_cpuhp_state. However, this is unstable because Malta itself does not support CPU hotplugging, whether via the legacy way or the modern way. Commit7aa563630bremoved .needed() check for vmstate_cpuhp_state, this broke the existing dependency that Malta had relied on, forcing Malta to save and load vmstate_cpuhp_state during the save/load process, which in turn caused a segmentation fault due to NULL fields in the stub-compiled code. Fix this by bringing back the .needed = cpuhp_needed callback for vmstate_cpuhp_state of PIIX4, that checks MachineClass::has_hotpluggable_cpus. Boards that do not support CPU hotplug (only MIPS Malta) will skip this subsection entirely, which is both correct and consistent with the previous behavior. At the same time, add a similar .needed() check to ICH9. Although no boards with ICH9 are affected by this issue, this helps avoid potential issues in the future. Reproducer (MIPS Malta): $ qemu-img create -f qcow2 dummy.qcow2 32M $ qemu-system-mipsel -nographic \ -drive if=none,format=qcow2,file=dummy.qcow2 [Type "C-a c" to get the "(qemu)" monitor prompt)] (qemu) savevm foo # segfault Reported-by: Peter Maydell <peter.maydell@linaro.org> Fixes:7aa563630b("pc: Start with modern CPU hotplug interface by default") Signed-off-by: Zhao Liu <zhao1.liu@intel.com> Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3360 Tested-by: Peter Maydell <peter.maydell@linaro.org> Link: https://lore.kernel.org/r/20260330053008.2721532-1-zhao1.liu@intel.com Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>