Re: [PATCH v4 3/3] LoongArch: KVM: Reject repeated PCH-PIC CTRL_INIT

[Bibo Mao <maobibo@loongson.cn>]

On 2026/10/16 上午7:46, Tao Cui wrote:
> From: Tao Cui <cuitao@kylinos.cn>
> 
> KVM_DEV_LOONGARCH_PCH_PIC_CTRL_INIT has no guard against repeated
> invocation: every call overwrites pch_pic_base and registers the same
> kvm_io_device on the MMIO bus at the new address, while
> kvm_pch_pic_destroy() unregisters only one bus range.  After a repeated
> init, MMIO to the stale ranges computes its register offset against the
> new base and silently reads 0 / drops writes, and the leftover bus
> entries persist until the VM is destroyed.
> 
> Reject repeated initialization with -EEXIST, using the initialized
> state of the kvm_io_device as the indicator.  The check, the MMIO base
> update and the bus registration are serialized by slots_lock, and the
> real registration error is propagated instead of being replaced with
> -EFAULT.
> 
> Fixes: d206d9514873 ("LoongArch: KVM: Add PCHPIC user mode read and write functions")
> Signed-off-by: Tao Cui <cuitao@kylinos.cn>
> ---
>   arch/loongarch/kvm/intc/pch_pic.c | 11 ++++++++---
>   1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/loongarch/kvm/intc/pch_pic.c b/arch/loongarch/kvm/intc/pch_pic.c
> index 51e4a6a39dc0..a4c35ed704be 100644
> --- a/arch/loongarch/kvm/intc/pch_pic.c
> +++ b/arch/loongarch/kvm/intc/pch_pic.c
> @@ -281,16 +281,21 @@ static int kvm_pch_pic_init(struct kvm_device *dev, u64 addr)
>   	struct kvm_io_device *device;
>   	struct loongarch_pch_pic *s = dev->kvm->arch.pch_pic;
>   
> -	s->pch_pic_base = addr;
>   	device = &s->device;
> +	mutex_lock(&kvm->slots_lock);
> +	if (s->device.ops) {
> +		ret = -EEXIST;
> +		goto out;
> +	}
> +	s->pch_pic_base = addr;
>   	/* init device by pch pic writing and reading ops */
>   	kvm_iodevice_init(device, &kvm_pch_pic_ops);
> -	mutex_lock(&kvm->slots_lock);
>   	/* register pch pic device */
>   	ret = kvm_io_bus_register_dev(kvm, KVM_MMIO_BUS, addr, PCH_PIC_SIZE, device);
> +out:
>   	mutex_unlock(&kvm->slots_lock);
one small nit, what to do if there is failure with 
kvm_io_bus_register_dev()?  clear s->pch_pic_base and  s->device.ops?

Regards
Bibo Mao
>   
> -	return (ret < 0) ? -EFAULT : 0;
> +	return ret;
>   }
>   
>   /* used by user space to get or set pch pic registers */
>