Multi-core support for RP2040 (Cortex-M0+)?

[TerryGeng]

One RP2040 has two cores and they are visible in https://github.com/zephyrproject-rtos/zephyr/blob/main/dts/arm/rpi_pico/rp2040.dtsi.

However, if I add CONFIG_MP_MAX_NUM_CPUS=2 into my prj.conf, the build fails with

.../zephyr/include/zephyr/arch/arm/asm_inline_gcc.h:53:2: error: #error "Cortex-M0 and Cortex-M0+ require SoC specific support for cross core synchronisation."
   53 | #error "Cortex-M0 and Cortex-M0+ require SoC specific support for cross core synchronisation."

Can I interpret this as the lack of multi-core support for RP2040? If that's the case, I would be quite surprised since RP2040 SDK has pretty good support for multi-core applications. What is the missing bit for zephyr to support multi-core on RP2040, or maybe I got something wrong?