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

[Tao Cui <cui.tao@linux.dev>]

在 2026/9/28 16:01, Bibo Mao 写道:
> 
> 
> On 2026/9/27 下午3:52, 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 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@kylinos.cn>
>> ---
>>   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.
> 
Thanks for the review.

Good point. Using `pch_pic_base == 0` as the initialization state mixes the device state with the configured address, a separate boolean is clearer.

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

I also agree that `-EEXIST` is a better fit than `-EBUSY` for repeated initialization. I'll update the patch accordingly.

Thanks,
Tao> 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 */
>>
>