Re: [PATCH v2 4/4] LoongArch: KVM: Reject repeated PCH-PIC CTRL_INIT

[Bibo Mao <maobibo@loongson.cn>]

On 2026/9/29 下午8:43, Huacai Chen wrote:
> Hi, Tao,
> 
> On Tue, Sep 29, 2026 at 6:29 PM Tao Cui <cui.tao@linux.dev> 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, tracking the state with
>> a has_init flag so the check and the MMIO base update are atomic
>> under slots_lock.  The base is only committed after a successful bus
>> registration, 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/include/asm/kvm_pch_pic.h |  1 +
>>   arch/loongarch/kvm/intc/pch_pic.c        | 12 ++++++++++--
>>   2 files changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/loongarch/include/asm/kvm_pch_pic.h b/arch/loongarch/include/asm/kvm_pch_pic.h
>> index 887b0431fd20..679132d840e6 100644
>> --- a/arch/loongarch/include/asm/kvm_pch_pic.h
>> +++ b/arch/loongarch/include/asm/kvm_pch_pic.h
>> @@ -53,6 +53,7 @@ struct loongarch_pch_pic {
>>          spinlock_t lock;
>>          struct kvm *kvm;
>>          struct kvm_io_device device;
>> +       bool has_init;
>>          union pch_pic_id id;
>>          uint64_t mask; /* 1:disable irq, 0:enable irq */
>>          uint64_t htmsi_en; /* 1:msi */
>> diff --git a/arch/loongarch/kvm/intc/pch_pic.c b/arch/loongarch/kvm/intc/pch_pic.c
>> index 7a704f18880d..a884a043feef 100644
>> --- a/arch/loongarch/kvm/intc/pch_pic.c
>> +++ b/arch/loongarch/kvm/intc/pch_pic.c
>> @@ -282,16 +282,24 @@ 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;
> Why so complicated? The below is enough, no?
> 
> diff --git a/arch/loongarch/kvm/intc/pch_pic.c
> b/arch/loongarch/kvm/intc/pch_pic.c
> index 2b63b0c2c7ce..7855d78304b7 100644
> --- a/arch/loongarch/kvm/intc/pch_pic.c
> +++ b/arch/loongarch/kvm/intc/pch_pic.c
> @@ -281,6 +281,9 @@ 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;
> 
> +       if (s->device->ops)
> +               return -EEXIST;
This can work, however I think that it is not a good idea to access 
internal structure field about kvm_io_device. If so, there is no use 
about API kvm_iodevice_init(), just s->device->ops = &kvm_pch_pic_ops is ok.

If adding has_init is redundant, maybe we can set s->pch_pic_base with 
INVALID_GPA in kvm_pch_pic_create() or some other methods. However I 
think directly accessing kvm_io_device::ops is not a good method, no 
other architectures do in such way.

Regards
Bibo Mao
> +
>          s->pch_pic_base = addr;
>          device = &s->device;
>          /* init device by pch pic writing and reading ops */
> 
>>
>> -       s->pch_pic_base = addr;
>>          device = &s->device;
>>          /* init device by pch pic writing and reading ops */
>>          kvm_iodevice_init(device, &kvm_pch_pic_ops);
>>          mutex_lock(&kvm->slots_lock);
>> +       if (s->has_init) {
>> +               ret = -EEXIST;
>> +               goto out;
>> +       }
>>          /* register pch pic device */
>>          ret = kvm_io_bus_register_dev(kvm, KVM_MMIO_BUS, addr, PCH_PIC_SIZE, device);
>> +       if (!ret) {
>> +               s->pch_pic_base = addr;
>> +               s->has_init = true;
>> +       }
>> +out:
>>          mutex_unlock(&kvm->slots_lock);
>>
>> -       return (ret < 0) ? -EFAULT : 0;
>> +       return ret;
>>   }
>>
>>   /* used by user space to get or set pch pic registers */
>> --
>> 2.43.0
>>