Re: [PATCH 2/2] KVM: PPC: Book3S HV: H_SVM_INIT_START must call UV_RETURN

[Laurent Dufour]

Le 20/03/2020 Ã 12:24, Bharata B Rao a ÃcritÂ:
> On Fri, Mar 20, 2020 at 11:26:43AM +0100, Laurent Dufour wrote:
> > When the call to UV_REGISTER_MEM_SLOT is failing, for instance because
> > there is not enough free secured memory, the Hypervisor (HV) has to call
> > UV_RETURN to report the error to the Ultravisor (UV). Then the UV will call
> > H_SVM_INIT_ABORT to abort the securing phase and go back to the calling VM.
> >
> > If the kvm->arch.secure_guest is not set, in the return path rfid is called
> > but there is no valid context to get back to the SVM since the Hcall has
> > been routed by the Ultravisor.
> >
> > Move the setting of kvm->arch.secure_guest earlier in
> > kvmppc_h_svm_init_start() so in the return path, UV_RETURN will be called
> > instead of rfid.
> >
> > Cc: Bharata B Rao <bharata@xxxxxxxxxxxxx>
> > Cc: Paul Mackerras <paulus@xxxxxxxxxx>
> > Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> > Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> > Signed-off-by: Laurent Dufour <ldufour@xxxxxxxxxxxxx>
> > ---
> >   arch/powerpc/kvm/book3s_hv_uvmem.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
> > index 79b1202b1c62..68dff151315c 100644
> > --- a/arch/powerpc/kvm/book3s_hv_uvmem.c
> > +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
> > @@ -209,6 +209,8 @@ unsigned long kvmppc_h_svm_init_start(struct kvm *kvm)
> >   	int ret = H_SUCCESS;
> >   	int srcu_idx;
> >   
> > +	kvm->arch.secure_guest = KVMPPC_SECURE_INIT_START;
> > +
> >   	if (!kvmppc_uvmem_bitmap)
> >   		return H_UNSUPPORTED;
> >   
> > @@ -233,7 +235,6 @@ unsigned long kvmppc_h_svm_init_start(struct kvm *kvm)
> >   			goto out;
> >   		}
> >   	}
> > -	kvm->arch.secure_guest |= KVMPPC_SECURE_INIT_START;
>
> There is an assumption that memory slots would have been registered with UV
> if KVMPPC_SECURE_INIT_START has been done. KVM_PPC_SVM_OFF ioctl will skip
> unregistration and other steps during reboot if KVMPPC_SECURE_INIT_START
> hasn't been done.
>
> Have you checked if that path isn't affected by this change?

I checked that and didn't find any issue there.

My only concern was that block:
	kvm_for_each_vcpu(i, vcpu, kvm) {
		spin_lock(&vcpu->arch.vpa_update_lock);
		unpin_vpa_reset(kvm, &vcpu->arch.dtl);
		unpin_vpa_reset(kvm, &vcpu->arch.slb_shadow);
		unpin_vpa_reset(kvm, &vcpu->arch.vpa);
		spin_unlock(&vcpu->arch.vpa_update_lock);
	}

But that seems to be safe.

However I'm not a familiar with the KVM's code, do you think an additional 
KVMPPC_SECURE_INIT_* value needed here?

Thanks,
Laurent.