Re: [PATCH] KVM: x86/hyperv: do not overwrite hc->ingpa for slow SIGNAL_EVENT hypercall

[Paolo Bonzini]

On Tue, Sep 22, 2026 at 12:52 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
> > diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> > index 9f5adcd26cba..e3a8e8236230 100644
> > --- a/arch/x86/kvm/hyperv.c
> > +++ b/arch/x86/kvm/hyperv.c
> > @@ -2501,6 +2501,7 @@ static int kvm_hvcall_signal_event(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *h
> >  {
> >       struct kvm_hv *hv = to_kvm_hv(vcpu->kvm);
> >       struct eventfd_ctx *eventfd;
> > +     u64 conn_id;
> >       int ret;
>
> This doesn't apply to any branch I can find, and there is some unnecessary variable
> shadowing going on here as well.
>
> The actual change looks good, but the diff is wonky.

You're right, I probably generated this from the wrong branch (or
machine). The right patch is at
https://lore.kernel.org/kvm/20260918135030.171564-2-pbonzini@xxxxxxxxxx/.

(BTW, I would like to talk about memory attributes and kvm-userfault
next Wednesday... and whether those are two different things at all).

Paolo


> >       ret = kvm_hv_hypercall_check_params(vcpu, hc);
> > @@ -2511,14 +2512,16 @@ static int kvm_hvcall_signal_event(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *h
> >               int ret;
> >               gpa_t gpa = hc->ingpa;
> >
> > -             if ((gpa & (__alignof__(hc->ingpa) - 1)) ||
> > -                 offset_in_page(gpa) + sizeof(hc->ingpa) > PAGE_SIZE)
> > +             if ((gpa & (__alignof__(conn_id) - 1)) ||
> > +                 offset_in_page(gpa) + sizeof(conn_id) > PAGE_SIZE)
> >                       return HV_STATUS_INVALID_ALIGNMENT;
> >
> >               ret = kvm_vcpu_read_guest(vcpu, gpa,
> > -                                       &hc->ingpa, sizeof(hc->ingpa));
> > +                                       &conn_id, sizeof(conn_id));
> >               if (ret < 0)
> >                       return HV_STATUS_INVALID_ALIGNMENT;
> > +     } else {
> > +             conn_id = hc->ingpa;
> >       }
> >
> >       /*
> > @@ -2526,15 +2529,15 @@ static int kvm_hvcall_signal_event(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *h
> >        * have no use for it, and in all known usecases it is zero, so just
> >        * report lookup failure if it isn't.
> >        */
> > -     if (hc->ingpa & 0xffff00000000ULL)
> > +     if (conn_id & 0xffff00000000ULL)
> >               return HV_STATUS_INVALID_PORT_ID;
> >       /* remaining bits are reserved-zero */
> > -     if (hc->ingpa & ~KVM_HYPERV_CONN_ID_MASK)
> > +     if (conn_id & ~KVM_HYPERV_CONN_ID_MASK)
> >               return HV_STATUS_INVALID_HYPERCALL_INPUT;
> >
> >       /* the eventfd is protected by vcpu->kvm->srcu, but conn_to_evt isn't */
> >       rcu_read_lock();
> > -     eventfd = idr_find(&hv->conn_to_evt, hc->ingpa);
> > +     eventfd = idr_find(&hv->conn_to_evt, conn_id);
> >       rcu_read_unlock();
> >       if (!eventfd)
> >               return HV_STATUS_INVALID_PORT_ID;
> > --
> > 2.52.0
> >
>