Re: [PATCH v3 3/3] LoongArch: KVM: Reject repeated PCH-PIC CTRL_INIT

[Huacai Chen]

Hi, Tao,

On Wed, Oct 14, 2026 at 1:30 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, using the initialized
> state of the kvm_io_device as the indicator.  The MMIO 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/kvm/intc/pch_pic.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/arch/loongarch/kvm/intc/pch_pic.c b/arch/loongarch/kvm/intc/pch_pic.c
> index 51e4a6a39dc0..7979466de729 100644
> --- a/arch/loongarch/kvm/intc/pch_pic.c
> +++ b/arch/loongarch/kvm/intc/pch_pic.c
> @@ -281,16 +281,22 @@ 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;
>         device = &s->device;
> +       mutex_lock(&kvm->slots_lock);
Why move the mutex_lock()?

Huacai

> +       if (s->device.ops) {
> +               ret = -EEXIST;
> +               goto out;
> +       }
>         /* init device by pch pic writing and reading ops */
>         kvm_iodevice_init(device, &kvm_pch_pic_ops);
> -       mutex_lock(&kvm->slots_lock);
>         /* 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;
> +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
>