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

[Huacai Chen]

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.


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
> >>
>