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

[Huacai Chen]

On Wed, Sep 30, 2026 at 5:03 PM Bibo Mao <maobibo@xxxxxxxxxxx> wrote:
>
>
>
> On 2026/9/30 下午4:52, Huacai Chen wrote:
> > On Wed, Sep 30, 2026 at 10:33 AM Bibo Mao <maobibo@xxxxxxxxxxx> wrote:
> >>
> >>
> >>
> >> On 2026/9/30 上午10:24, Huacai Chen wrote:
> >>> On Wed, Sep 30, 2026 at 9:53 AM Bibo Mao <maobibo@xxxxxxxxxxx> 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@xxxxxxxxx> 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 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@xxxxxxxxxx>
> >>>>>> ---
> >>>>>>     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.
OK, Tao, please update your code, drop the 2nd patch and simplify the
4th one. Thanks.

Huacai

>
> >
> >
> > 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
> >>>>>>
> >>>>
> >>
> >>
>