Re: [PATCH] hw/loongarch/virt: Add reset interface for virt-machine

[Peter Maydell]

On Thu, 31 Oct 2024 at 06:55, Bibo Mao <maobibo@loongson.cn> wrote:
>
> With generic cpu reset interface, pc register is entry of FLASH for
> UEFI BIOS. However with direct kernel booting requirement, there is
> little different, pc register of primary cpu is entry address of ELF
> file.
>
> At the same time with requirement of cpu hotplug, hot-added CPU should
> register reset interface for this cpu object. Now reset callback is
> not registered for hot-added CPU.
>
> With this patch reset callback for CPU is register when CPU instance
> is created, and reset interface is added for virt-machine board. In
> reset interface of virt-machine, reset for direct kernel booting
> requirement is called.
>
> Signed-off-by: Bibo Mao <maobibo@loongson.cn>
> ---
>  hw/loongarch/boot.c         |  9 +--------
>  hw/loongarch/virt.c         | 14 ++++++++++++++
>  include/hw/loongarch/boot.h |  1 +
>  target/loongarch/cpu.c      | 10 ++++++++++
>  4 files changed, 26 insertions(+), 8 deletions(-)
>
> diff --git a/hw/loongarch/boot.c b/hw/loongarch/boot.c
> index cb668703bd..cbb4e3737d 100644
> --- a/hw/loongarch/boot.c
> +++ b/hw/loongarch/boot.c
> @@ -216,12 +216,11 @@ static int64_t load_kernel_info(struct 
> loongarch_boot_info *info)
>      return kernel_entry;
>  }
>
> -static void reset_load_elf(void *opaque)
> +void reset_load_elf(void *opaque)
>  {
>      LoongArchCPU *cpu = opaque;
>      CPULoongArchState *env = &cpu->env;
>
> -    cpu_reset(CPU(cpu));
>      if (env->load_elf) {
>         if (cpu == LOONGARCH_CPU(first_cpu)) {
>              env->gpr[4] = env->boot_info->a0;
> @@ -320,12 +319,6 @@ static void loongarch_direct_kernel_boot(struct 
> loongarch_boot_info *info)
>  void loongarch_load_kernel(MachineState *ms, struct loongarch_boot_info 
> *info)
>  {
>      LoongArchVirtMachineState *lvms = LOONGARCH_VIRT_MACHINE(ms);
> -    int i;
> -
> -    /* register reset function */
> -    for (i = 0; i < ms->smp.cpus; i++) {
> -        qemu_register_reset(reset_load_elf, LOONGARCH_CPU(qemu_get_cpu(i)));
> -    }
>
>      info->kernel_filename = ms->kernel_filename;
>      info->kernel_cmdline = ms->kernel_cmdline;
> diff --git a/hw/loongarch/virt.c b/hw/loongarch/virt.c
> index 9a635d1d3d..80680d178c 100644
> --- a/hw/loongarch/virt.c
> +++ b/hw/loongarch/virt.c
> @@ -1434,6 +1434,19 @@ static int64_t virt_get_default_cpu_node_id(const 
> MachineState *ms, int idx)
>      }
>  }
>
> +static void virt_reset(MachineState *machine, ResetType type)
> +{
> +    CPUState *cs;
> +
> +    /* Reset all devices including CPU devices */
> +    qemu_devices_reset(type);
> +
> +    /* Reset PC and register context for kernel direct booting method */
> +    CPU_FOREACH(cs) {
> +        reset_load_elf(LOONGARCH_CPU(cs));
> +    }
> +}
> +
>  static void virt_class_init(ObjectClass *oc, void *data)
>  {
>      MachineClass *mc = MACHINE_CLASS(oc);
> @@ -1457,6 +1470,7 @@ static void virt_class_init(ObjectClass *oc, void *data)
>      mc->auto_enable_numa_with_memdev = true;
>      mc->get_hotplug_handler = virt_get_hotplug_handler;
>      mc->default_nic = "virtio-net-pci";
> +    mc->reset = virt_reset;
>      hc->plug = virt_device_plug_cb;
>      hc->pre_plug = virt_device_pre_plug;
>      hc->unplug_request = virt_device_unplug_request;
> diff --git a/include/hw/loongarch/boot.h b/include/hw/loongarch/boot.h
> index b3b870df1f..c7020ec9bb 100644
> --- a/include/hw/loongarch/boot.h
> +++ b/include/hw/loongarch/boot.h
> @@ -115,5 +115,6 @@ struct memmap_entry {
>  };
>
>  void loongarch_load_kernel(MachineState *ms, struct loongarch_boot_info 
> *info);
> +void reset_load_elf(void *opaque);
>
>  #endif /* HW_LOONGARCH_BOOT_H */
> diff --git a/target/loongarch/cpu.c b/target/loongarch/cpu.c
> index 7212fb5f8f..f7f8fcc024 100644
> --- a/target/loongarch/cpu.c
> +++ b/target/loongarch/cpu.c
> @@ -592,6 +592,13 @@ static void loongarch_cpu_disas_set_info(CPUState *s, 
> disassemble_info *info)
>      info->print_insn = print_insn_loongarch;
>  }
>
> +#ifndef CONFIG_USER_ONLY
> +static void loongarch_cpu_reset_cb(void *opaque)
> +{
> +    cpu_reset((CPUState *) opaque);
> +}
> +#endif
> +
>  static void loongarch_cpu_realizefn(DeviceState *dev, Error **errp)
>  {
>      CPUState *cs = CPU(dev);
> @@ -607,6 +614,9 @@ static void loongarch_cpu_realizefn(DeviceState *dev, 
> Error **errp)
>      loongarch_cpu_register_gdb_regs_for_features(cs);
>
>      cpu_reset(cs);
> +#ifndef CONFIG_USER_ONLY
> +    qemu_register_reset(loongarch_cpu_reset_cb, dev);
> +#endif

Please don't add new uses of qemu_register_reset().
I know that CPU reset is currently rather awkward (because
we don't automatically-reset CPU objects the way we do most
device objects), but generally what should happen is that
the machine model should arrange to reset the CPU objects
it creates. (Which is what it looks like the code you're
removing in this patch was doing already.)

thanks
-- PMM