Re: [PATCH v2] hw/loongarch/virt: Add reset interface for virt-machine

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

Hi Bibo,

On 1/9/25 10:19, Bibo Mao wrote:
> With generic cpu reset interface, pc register is entry of FLASH for
> UEFI BIOS. However with direct kernel booting requirement, there is
> a 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>
> ---
> v1 ... v2:
>    1. Add qemu_unregister_reset() in function loongarch_cpu_unrealizefn(),
>       remove reset callback if vCPU is unrealized.
> ---
> 
> 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      | 11 +++++++++++
>   4 files changed, 27 insertions(+), 8 deletions(-)
> 
> diff --git a/hw/loongarch/boot.c b/hw/loongarch/boot.c
> index 14d6c52d4e..4919758a20 100644
> --- a/hw/loongarch/boot.c
> +++ b/hw/loongarch/boot.c
> @@ -324,12 +324,11 @@ 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;
> @@ -429,12 +428,6 @@ static void loongarch_direct_kernel_boot(MachineState *ms,
>   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)));

I agree CPU reset shouldn't be part of loading code to memory.

> -    }
>   
>       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 b15ada2078..4fc8506c10 100644
> --- a/hw/loongarch/virt.c
> +++ b/hw/loongarch/virt.c
> @@ -1199,6 +1199,19 @@ 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, const void *data)
>   {
>       MachineClass *mc = MACHINE_CLASS(oc);
> @@ -1223,6 +1236,7 @@ static void virt_class_init(ObjectClass *oc, const void *data)
>       mc->has_hotpluggable_cpus = 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 9819f7fbe3..386b4406ad 100644
> --- a/include/hw/loongarch/boot.h
> +++ b/include/hw/loongarch/boot.h
> @@ -114,5 +114,6 @@ 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 3a7621c0ea..61c8acb3c2 100644
> --- a/target/loongarch/cpu.c
> +++ b/target/loongarch/cpu.c
> @@ -652,6 +652,13 @@ 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);
> @@ -668,6 +675,9 @@ static void loongarch_cpu_realizefn(DeviceState *dev, Error **errp)
>   
>       qemu_init_vcpu(cs);
>       cpu_reset(cs);

Devices shouldn't call their DeviceReset handler manually, as it is
always called after DeviceRealize.

> +#ifndef CONFIG_USER_ONLY
> +    qemu_register_reset(loongarch_cpu_reset_cb, dev);

qemu_register_reset() is a legacy API, replaced by
qemu_register_resettable().

That said, I don't think the CPU object has to register its own
reset handlers. Instead that should the be responsibility of the
object creating the CPU objects.

> +#endif
>   
>       lacc->parent_realize(dev, errp);
>   }
> @@ -678,6 +688,7 @@ static void loongarch_cpu_unrealizefn(DeviceState *dev)
>   
>   #ifndef CONFIG_USER_ONLY
>       cpu_remove_sync(CPU(dev));
> +    qemu_unregister_reset(loongarch_cpu_reset_cb, dev);

Ditto, legacy -> qemu_unregister_resettable().

>   #endif
>   
>       lacc->parent_unrealize(dev);
> 
> base-commit: 91589bcd9fee0e66b241d04e5f37cd4f218187a2