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

[Bibo Mao <maobibo@loongson.cn>]

On 2026/9/30 下午4:52, Huacai Chen wrote:
> On Wed, Sep 30, 2026 at 10:33 AM Bibo Mao <maobibo@loongson.cn> wrote:
>>
>>
>>
>> On 2026/9/30 上午10:24, Huacai Chen wrote:
>>> On Wed, Sep 30, 2026 at 9:53 AM Bibo Mao <maobibo@loongson.cn> wrote:
>>>>
>>>>
>>>>
>>>> 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.
>>> I'm a little not agree. :)
>>>
>>> I think kvm_iodevice_init() is designed to do more work rather than
>>> just set the ops (though it just set the ops now), otherwise its name
>>> should be kvm_iodevice_set_ops().
>>>
>>> In addition, even if kvm_iodevice_init() is really a setter, there is
>>> no getter for the ops, so when we need to access ops, we can only
>>> open-code it.
>> if so, you can try to add kvm_iodevice_get_ops API and check the
>> response of KVM community.
> There is not a setter, so I don't think a getter is necessary.
why setter is necessary, getter is not necessary.
> 
> Moreover, you said "no other architectures directly access ops", but
> in fact, __vgic_doorbell_to_its() from arch/arm64/kvm/vgic/vgic-its.c
> directly accesses ops.
If it is used by others, I have no objection any more. But for me I 
never write such code.

> 
> 
> Huacai
> 
>>
>> Regards
>> Bibo Mao
>>>
>>>
>>> Huacai
>>>
>>>>
>>>> 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
>>>>>>
>>>>
>>
>>