Re: [PATCH 6/6] LoongArch: KVM: Reject repeated PCH-PIC CTRL_INIT

[Bibo Mao]

On 2026/9/27 下午3:52, Tao Cui wrote:
> From: Tao Cui <cuitao@xxxxxxxxxx>
>
> 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 a repeated init with -EBUSY, a null address with -EINVAL, and
> only set pch_pic_base after the bus registration succeeds so a failed
> init does not leave the device half-initialized.  The 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@xxxxxxxxxx>
> ---
>   arch/loongarch/kvm/intc/pch_pic.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/arch/loongarch/kvm/intc/pch_pic.c b/arch/loongarch/kvm/intc/pch_pic.c
> index 136211f154d4..2baf9ecf0c8a 100644
> --- a/arch/loongarch/kvm/intc/pch_pic.c
> +++ b/arch/loongarch/kvm/intc/pch_pic.c
> @@ -285,7 +285,10 @@ 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;
> +	if (!addr)
> +		return -EINVAL;
To detect repeated init, I think it will be better add a BOOL type 
variable such ready/has_init for this. In theory device with physical 
address 0 is possible.

> +	if (s->pch_pic_base)
> +		return -EBUSY;
-EEXIST or 0 if it is created already?

Regards
Bibo Mao
>   	device = &s->device;
>   	/* init device by pch pic writing and reading ops */
>   	kvm_iodevice_init(device, &kvm_pch_pic_ops);
> @@ -293,8 +296,11 @@ static int kvm_pch_pic_init(struct kvm_device *dev, u64 addr)
>   	/* register pch pic device */
>   	ret = kvm_io_bus_register_dev(kvm, KVM_MMIO_BUS, addr, PCH_PIC_SIZE, device);
>   	mutex_unlock(&kvm->slots_lock);
> +	if (ret < 0)
> +		return ret;
>   
> -	return (ret < 0) ? -EFAULT : 0;
> +	s->pch_pic_base = addr;
> +	return 0;
>   }
>   
>   /* used by user space to get or set pch pic registers */