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

[Huacai Chen]

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;
+
        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
>