QEMU start failed when smp cpu < smp maxcpus , because qemu send a NULL
cpu to KVM, this patch adds a check for kvm_ipi_access_regs() to fix it.

run with '-smp 1,maxcpus=4,sockets=4,cores=1,threads=1'

we got:
Unexpected error in kvm_device_access() at ../accel/kvm/kvm-all.c:3477:
qemu-system-loongarch64: KVM_SET_DEVICE_ATTR failed: Group 1073741825 attr 0x0000000000010000: Invalid argument

Signed-off-by: Song Gao <gaosong@loongson.cn>
---
 hw/intc/loongarch_ipi_kvm.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/hw/intc/loongarch_ipi_kvm.c b/hw/intc/loongarch_ipi_kvm.c
index 4cb3acc921..dd4c367abf 100644
--- a/hw/intc/loongarch_ipi_kvm.c
+++ b/hw/intc/loongarch_ipi_kvm.c
@@ -23,36 +23,41 @@ static void kvm_ipi_access_regs(void *opaque, bool write)
     LoongarchIPIState *lis = LOONGARCH_IPI(opaque);
     IPICore *core;
     uint64_t attr;
-    int cpu, fd = lis->dev_fd;
+    int i, cpu_index, fd = lis->dev_fd;
 
     if (fd == 0) {
         return;
     }
 
-    for (cpu = 0; cpu < ipi->num_cpu; cpu++) {
-        core = &ipi->cpu[cpu];
-        attr = (cpu << 16) | CORE_STATUS_OFF;
+    for (i = 0; i < ipi->num_cpu; i++) {
+        core = &ipi->cpu[i];
+        if (core->cpu == NULL) {
+            continue;
+        }
+        cpu_index = i;
+
+        attr = (cpu_index << 16) | CORE_STATUS_OFF;
         kvm_ipi_access_reg(fd, attr, &core->status, write);
 
-        attr = (cpu << 16) | CORE_EN_OFF;
+        attr = (cpu_index << 16) | CORE_EN_OFF;
         kvm_ipi_access_reg(fd, attr, &core->en, write);
 
-        attr = (cpu << 16) | CORE_SET_OFF;
+        attr = (cpu_index << 16) | CORE_SET_OFF;
         kvm_ipi_access_reg(fd, attr, &core->set, write);
 
-        attr = (cpu << 16) | CORE_CLEAR_OFF;
+        attr = (cpu_index << 16) | CORE_CLEAR_OFF;
         kvm_ipi_access_reg(fd, attr, &core->clear, write);
 
-        attr = (cpu << 16) | CORE_BUF_20;
+        attr = (cpu_index << 16) | CORE_BUF_20;
         kvm_ipi_access_reg(fd, attr, &core->buf[0], write);
 
-        attr = (cpu << 16) | CORE_BUF_28;
+        attr = (cpu_index << 16) | CORE_BUF_28;
         kvm_ipi_access_reg(fd, attr, &core->buf[2], write);
 
-        attr = (cpu << 16) | CORE_BUF_30;
+        attr = (cpu_index << 16) | CORE_BUF_30;
         kvm_ipi_access_reg(fd, attr, &core->buf[4], write);
 
-        attr = (cpu << 16) | CORE_BUF_38;
+        attr = (cpu_index << 16) | CORE_BUF_38;
         kvm_ipi_access_reg(fd, attr, &core->buf[6], write);
     }
 }
-- 
2.43.0

On 2025/7/25 下午4:12, Song Gao wrote:
> QEMU start failed when smp cpu < smp maxcpus , because qemu send a NULL
> cpu to KVM, this patch adds a check for kvm_ipi_access_regs() to fix it.
> 
> run with '-smp 1,maxcpus=4,sockets=4,cores=1,threads=1'
> 
> we got:
> Unexpected error in kvm_device_access() at ../accel/kvm/kvm-all.c:3477:
> qemu-system-loongarch64: KVM_SET_DEVICE_ATTR failed: Group 1073741825 attr 0x0000000000010000: Invalid argument
> 
> Signed-off-by: Song Gao <gaosong@loongson.cn>
> ---
>   hw/intc/loongarch_ipi_kvm.c | 27 ++++++++++++++++-----------
>   1 file changed, 16 insertions(+), 11 deletions(-)
> 
> diff --git a/hw/intc/loongarch_ipi_kvm.c b/hw/intc/loongarch_ipi_kvm.c
> index 4cb3acc921..dd4c367abf 100644
> --- a/hw/intc/loongarch_ipi_kvm.c
> +++ b/hw/intc/loongarch_ipi_kvm.c
> @@ -23,36 +23,41 @@ static void kvm_ipi_access_regs(void *opaque, bool write)
>       LoongarchIPIState *lis = LOONGARCH_IPI(opaque);
>       IPICore *core;
>       uint64_t attr;
> -    int cpu, fd = lis->dev_fd;
> +    int i, cpu_index, fd = lis->dev_fd;
>   
>       if (fd == 0) {
>           return;
>       }
>   
> -    for (cpu = 0; cpu < ipi->num_cpu; cpu++) {
> -        core = &ipi->cpu[cpu];
> -        attr = (cpu << 16) | CORE_STATUS_OFF;
> +    for (i = 0; i < ipi->num_cpu; i++) {
> +        core = &ipi->cpu[i];
> +        if (core->cpu == NULL) {
> +            continue;
> +        }
> +        cpu_index = i;
> +
> +        attr = (cpu_index << 16) | CORE_STATUS_OFF;
>           kvm_ipi_access_reg(fd, attr, &core->status, write);
>   
> -        attr = (cpu << 16) | CORE_EN_OFF;
> +        attr = (cpu_index << 16) | CORE_EN_OFF;
>           kvm_ipi_access_reg(fd, attr, &core->en, write);
>   
> -        attr = (cpu << 16) | CORE_SET_OFF;
> +        attr = (cpu_index << 16) | CORE_SET_OFF;
>           kvm_ipi_access_reg(fd, attr, &core->set, write);
>   
> -        attr = (cpu << 16) | CORE_CLEAR_OFF;
> +        attr = (cpu_index << 16) | CORE_CLEAR_OFF;
>           kvm_ipi_access_reg(fd, attr, &core->clear, write);
>   
> -        attr = (cpu << 16) | CORE_BUF_20;
> +        attr = (cpu_index << 16) | CORE_BUF_20;
>           kvm_ipi_access_reg(fd, attr, &core->buf[0], write);
>   
> -        attr = (cpu << 16) | CORE_BUF_28;
> +        attr = (cpu_index << 16) | CORE_BUF_28;
>           kvm_ipi_access_reg(fd, attr, &core->buf[2], write);
>   
> -        attr = (cpu << 16) | CORE_BUF_30;
> +        attr = (cpu_index << 16) | CORE_BUF_30;
>           kvm_ipi_access_reg(fd, attr, &core->buf[4], write);
>   
> -        attr = (cpu << 16) | CORE_BUF_38;
> +        attr = (cpu_index << 16) | CORE_BUF_38;
>           kvm_ipi_access_reg(fd, attr, &core->buf[6], write);
>       }
>   }
> 
Reviewed-by: Bibo Mao <maobibo@loongson.cn>