Re: [PATCH] hw/loongarch/virt: Fix the cpu hotplug issue

[Bibo Mao]

On 2025/9/1 下午7:58, Igor Mammedov wrote:
On Fri, 29 Aug 2025 10:31:57 +0800
Bibo Mao <maob...@loongson.cn> wrote:

On 2025/8/29 上午9:32, Xianglai Li wrote:
The hot-plugged cpu does not register the cpu reset function, so the cpu
plugged in later cannot reset properly, and there will be problems when
restarting.

Now register the cpu reset function in the cpu hotplug callback function.
Oh, it is actually one problem and it is missing :(. There is similiar
patch posted at:
  
https://lore.kernel.org/qemu-devel/20241031065418.3111892-1-maob...@loongson.cn/

I prefer to adding cpu reset in CPU object realize function rather
hotplug handler, and executing reset_load_elf() in board specific
reset callback. However peter has different thoughts.

this patch and above mentioned one expose direct boot specific
reset_load_elf() on a generic hardware bring up path. That's
probably isn't right.

Ideally default (cpu_reset()) reset would happen 1st during
cpu creation/board init and then direct boot would patch
the CPU that actually would execute payload.

PS:
what's the reason to call reset_load_elf() on all present
vCPUs and why hotplugged ones matter here?

Shouldn't direct booted QEMU patch BSP only?
yes, reset_load_elf() is only BSP relative, now BSP directly jumps
to kernel entry, AP jump to slave_boot_code[]. Ideally both BSP and
AP can jump to aux boot code if it boot code works like EFI bios, then 
reset_load_elf() is not necessary for BSP also. I will try it.

Regards
Bibo Mao



Regards
Bibo Mao

Signed-off-by: Xianglai Li <lixiang...@loongson.cn>
---
   hw/loongarch/boot.c         | 8 +-------
   hw/loongarch/virt.c         | 4 ++++
   include/hw/loongarch/virt.h | 1 +
   3 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/hw/loongarch/boot.c b/hw/loongarch/boot.c
index 14d6c52d4e..6bc1f3d50c 100644
--- a/hw/loongarch/boot.c
+++ b/hw/loongarch/boot.c
@@ -324,7 +324,7 @@ 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;
@@ -429,12 +429,6 @@ 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)));
-    }
   
       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..71f8ddc980 100644
--- a/hw/loongarch/virt.c
+++ b/hw/loongarch/virt.c
@@ -1013,6 +1013,8 @@ static void virt_cpu_unplug(HotplugHandler *hotplug_dev,
       /* Notify acpi ged CPU removed */
       hotplug_handler_unplug(HOTPLUG_HANDLER(lvms->acpi_ged), dev, 
&error_abort);
   
+    /* unregister reset function */
+    qemu_unregister_reset(reset_load_elf, cpu);
       cpu_slot = virt_find_cpu_slot(MACHINE(lvms), cpu->phy_id);
       cpu_slot->cpu = NULL;
   }
@@ -1037,6 +1039,8 @@ static void virt_cpu_plug(HotplugHandler *hotplug_dev,
                                &error_abort);
       }
   
+    /* register reset function */
+    qemu_register_reset(reset_load_elf, cpu);
       cpu_slot = virt_find_cpu_slot(MACHINE(lvms), cpu->phy_id);
       cpu_slot->cpu = CPU(dev);
   }
diff --git a/include/hw/loongarch/virt.h b/include/hw/loongarch/virt.h
index 602feab0f0..15ea393386 100644
--- a/include/hw/loongarch/virt.h
+++ b/include/hw/loongarch/virt.h
@@ -71,6 +71,7 @@ struct LoongArchVirtMachineState {
   OBJECT_DECLARE_SIMPLE_TYPE(LoongArchVirtMachineState, LOONGARCH_VIRT_MACHINE)
   void virt_acpi_setup(LoongArchVirtMachineState *lvms);
   void virt_fdt_setup(LoongArchVirtMachineState *lvms);
+void reset_load_elf(void *opaque);
   
   static inline bool virt_is_veiointc_enabled(LoongArchVirtMachineState *lvms)
   {